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  • 1.
    Varmuza, Kurt
    et al.
    Vienna University of Technology, Austria.
    Filzmoser, Peter
    Vienna University of Technology, Austria.
    Fray, Nicolas
    Université de Paris, France.
    Cottin, Herve
    Université de Paris, France.
    Merouane, Siane
    Max-Planck-Institute, Germany.
    Stenzel, Oliver
    Max-Planck-Institute, Germany.
    Paquette, John
    Max-Planck-Institute, Germany.
    Kissel, Jochen
    Max-Planck-Institute, Germany.
    Briois, Christelle
    Université d'Orléans, France.
    Baklouti, Donia
    Université Paris Sud, France.
    Bardyn, Anais
    University of Maryland, USA.
    Siljeström, Sandra
    RISE Research Institutes of Sweden, Material och produktion, Kemi, biomaterial och textil.
    Silén, Johan
    Finnish Meteorological Institute, Finland.
    Hilchenbach, Martin
    Max-Planck-Institute, Germany.
    Composition of cometary particles collected during two periods of the Rosetta mission: multivariate evaluation of mass spectral data2020Ingår i: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, artikel-id e3218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The instrument COSIMA (COmetary Secondary Ion Mass Analyzer) onboard of the European Space Agency mission Rosetta collected and analyzed dust particles in the neighborhood of comet 67P/Churyumov-Gerasimenko. The chemical composition of the particle surfaces was characterized by time-of-flight secondary ion mass spectrometry. A set of 2213 spectra has been selected, and relative abundances for CH-containing positive ions as well as positive elemental ions define a set of multivariate data with nine variables. Evaluation by complementary chemometric techniques shows different compositions of sample groups collected during two periods of the mission. The first period was August to November 2014 (far from the Sun); the second period was January 2015 to February 2016 (nearer to the Sun). The applied data evaluation methods consider the compositional nature of the mass spectral data and comprise robust principal component analysis as well as classification with discriminant partial least squares regression, k-nearest neighbor search, and random forest decision trees. The results indicate a high importance of the relative abundances of the secondary ions C+ and Fe+ for the group separation and demonstrate an enhanced content of carbon-containing substances in samples collected in the period with smaller distances to the Sun. © 2020 The Authors.

  • 2.
    Varmuza, Kurt
    et al.
    Vienna University of Technology, Austria.
    Filzmoser, Peter
    Vienna University of Technology, Austria.
    Hoffmann, Irene
    Vienna University of Technology, Austria.
    Walach, Jan
    Vienna University of Technology, Austria.
    Cottin, Herve
    Université Paris‐Est Créteil et Université Paris, France.
    Fray, Nicolas
    Université Paris‐Est Créteil et Université Paris, France.
    Briois, Christelle
    Université d'Orléans, France.
    Modica, Paola
    Université d'Orléans, France.
    Bardyn, Anais
    Carnegie Institution of Washington, USA.
    Silén, Johan
    Finnish Meteorological Institute, Finland.
    Siljeström, Sandra
    RISE - Research Institutes of Sweden, Biovetenskap och material, Kemi och material.
    Stenzel, Oliver
    Max-Planck-Institute for Solar System Research, Germany.
    Kissel, Jochen
    Max-Planck-Institute for Solar System Research, Germany.
    Hilchenbach, Martin
    Max-Planck-Institute for Solar System Research, Germany.
    Significance of variables for discrimination: Applied to the search of organic ions in mass spectra measured on cometary particles2018Ingår i: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 32, nr 4, artikel-id e3001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The instrument Cometary Secondary Ion Mass Analyzer (COSIMA) on board of the European Space Agency mission Rosetta to the comet 67P/Churyumov-Gerasimenko is a secondary ion mass spectrometer with a time-of-flight mass analyzer. It collected near the comet several thousand particles, imaged them, and analyzed the elemental and chemical compositions of their surfaces. In this study, variables have been generated from the spectral data covering the mass ranges of potential C-, H-, N-, and O-containing ions. The variable importance in binary discriminations between spectra measured on cometary particles and those measured on the target background has been estimated by the univariate t test and the multivariate methods discriminant partial least squares, random forest, and a robust method based on the log ratios of all variable pairs. The results confirm the presence of organic substances in cometary matter-probably a complex macromolecular mixture.

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