1,721,884 research outputs found
Asuka 12236 more primitive than Paris: Clues given by their Infrared and Raman micro‐spectroscopy signatures
No full textInternational audienceCarbonaceous chondrites are meteorites originating from undifferentiated objects of the Solar System, which may retain signatures of primitive matter. Here, we present a comparative study between two CM chondrites Asuka 12236 and Paris, both considered among the most primitive in the carbonaceous chondrite meteorite collection. This work is based on the combination of infrared and Raman micro-spectroscopy, aiming to compare the spectral characteristics of these two peculiar chondrites. We present an average infrared spectrum from the mid to far infrared of Asuka 12236, which has never been reported yet in the literature. Contrary to the average spectrum of Paris, the Asuka 12236 spectrum shows signatures of anhydrous minerals (olivine and or pyroxene) as well as the presence of amorphous phases. These findings are in agreement with the low degree of alteration reported for Asuka 12236. Aromatic primary amines and imines are also detected in Asuka 12236, heterogeneously distributed within the meteorite. In addition, the comparison of the Raman signatures of the two meteorites highlights different carbon structuration and thus thermal histories. Our spectroscopic investigations confirm that Asuka 12236 can be considered more primitive than the Paris carbonaceous chondrite.</div
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The most primitive CM chondrites, Asuka 12085, 12169, and 12236, of subtypes 3.0–2.8: Their characteristic features and classification
Get PDFCM chondrites (CMs) are the most abundant group of carbonaceous chondrites. CMs experienced varying degrees of secondary aqueous alteration and heating that modified or destroyed their primitive features. We have studied three chondrites, Asuka (A) 12085, A 12169, and A 12236. Their modal compositions, chondrule size distributions, and bulk composition indicate that they are CMs. However, the common occurrence of melilite in CAIs and glass in chondrules, abundant Fe–Ni metal, the absence of tochilinite-cronstedtite intergrowths, and almost no phyllosilicates, all suggest that these chondrites, especially A 12169, experienced only minimal aqueous alteration. The textures and compositions of metal and sulfides, the lack of ferroan rims on AOA olivines, the compositional distribution of ferroan olivine, and the Raman spectra of their matrices, indicate that these chondrites experienced neither significant heating nor dehydration. These chondrites, especially A 12169, are the most primitive CMs so far reported. The degree of the alteration increases from A 12169, through A 12236, to A 12085. We propose the criteria for subtypes of 3.0–2.8 for CMs. A 12169, A 12236, and A 12085 are classified as subtype 3.0, 2.9, and 2.8, respectively. The oxygen isotopic composition of the Asuka CMs is consistent with these samples having experienced only a limited degree of aqueous alteration. The CM and CO groups are probably not derived from a single heterogeneous parent body. These chondrites are also of particular significance in view of the imminent return of sample material from the asteroids Ryugu and Bennu
Assessing the Effect of Aqueous Alteration on Soluble Organic Matter in Primitive Carbonaceous Chondrites: The Case of Asuka 12236
No full textCarbonaceous chondrites (CCs) are considered the closest
solid
material to the composition of the early Solar System and can provide
information about the origin of organic matter (OM) in the system
and on Earth. Despite being primitive, their parent bodies have undergone
secondary processes shortly after their formation (hydrothermal or
metamorphism alterations) that blur their initial organic or mineral
composition. The most primitive CC members are hence very precious
to study the original composition. Here, we report the characterization
of the soluble organic matter (SOM) of Asuka 12236, classified among
the most primitive members of the CM group in comparison with the
SOM from other CM chondrites: Paris, Murchison, and Aguas Zarcas.
Analysis of these SOM were performed using several analytical techniques,
including elemental analysis, high-resolution mass spectrometry, and
liquid chromatography coupled to different mass spectrometers. Our
results show that Asuka 12236 has the lowest H content among the CMs
studied here and presents heterogeneity in its C content, likely indicating
variable degrees of aqueous alteration. High-resolution mass spectrometry
analysis reveals that Asuka 12236 has a molecular diversity similar
to the SOM of Murchison and Aguas Zarcas but with a higher abundance
of sulfur compounds, more similar to Paris SOM. The content of organomagnesium
compounds indicates no high-pressure or -temperature stress but rather
mid-temperature aqueous alteration for Asuka 12236, like Murchison
SOM, but unlike Paris or Aguas Zarcas SOM. From liquid chromatography
coupled with mass spectrometry analysis, we observed the highest concentration
of amino acids in Asuka 12236 compared to the other CM chondrites
considered here. Amino acids are mainly of α forms, witnessing
a Strecker formation or a formose-type reaction under low amounts
of water, in agreement with the low H content recorded in this peculiar
chondrite. This study of the SOM of chondrites with different degrees
of alteration highlights that organic compounds may be transformed
much more rapidly than the minerals during hydrothermal alteration.
This OM evolution depends on the amount of water and/or the temperature
and/or pressure, leading toward significant transformation from one
chondrite to another, while the mineralogy can indicate a low degree
of alteration. In addition, to better assess the initial OM in chondrites,
the impact of aqueous alteration on organic matter calls for additional
laboratory experimentation
Assessing the effect of aqueous alteration on soluble organic matter in primitive carbonaceous chondrites: the case of Asuka 12236
No full textInternational audienceCarbonaceous chondrites (CC) are considered the closest solid material to the composition of the early Solar System and can provide information on the origin of organic matter (OM) in the system and on Earth. Despite being primitive, their parent bodies have undergone secondary processes shortly after their formation (hydrothermal or metamorphism alterations) that blur their initial organic or mineral composition. The most primitive CC members are hence very precious to study the original composition. Here, we report the characterisation of the soluble organic matter (SOM) of Asuka 12236 classified among the most primitive members of the CM group in comparison with the SOM from other CM chondrites: Paris, Murchison and Aguas Zarcas. Analysis of these SOM were performed using several analytical techniques including elemental analysis, high resolution mass spectrometry and liquid chromatography coupled to different mass spectrometers. Our results show that Asuka 12236 has the lowest H content among the CMs studied here, and presents heterogeneity in its C content, likely indicating variable degrees of aqueous alteration. High resolution mass spectrometry analysis reveals that Asuka 12236 has a molecular diversity similar to the SOM of Murchison and Aguas Zarcas but with higher abundance of sulfur compounds more similar to Paris SOM. The content of organomagnesiumcompounds indicates no high pressure or temperature stress but rather mid-temperature aqueous alteration for Asuka 12236, like Murchison SOM, but unlike Paris or Aguas Zarcas SOM. From liquid chromatography coupled with mass spectrometry analysis, we observed the highest concentration of amino acids in Asuka 12236 compared to the other CM chondrites considered here. Amino acids are mainly of alpha forms, witnessing of a Strecker formation or a formose-type reaction under low amounts of water, in agreement with the low H content recorded in this peculiar chondrite. This study of the SOM of chondrites with different alteration degrees highlights that organic compounds may be transformed much more rapidly than the minerals during hydrothermal alteration. This OM evolution depends on the amount of water and/or the temperature and/or pressure, leading towards significant transformation from one chondrite to another while the mineralogy can indicate a low degree of alteration. In addition to better assess the initial OM in chondrites, the impact of aqueous alteration on organic matter calls for additional laboratory experimentation
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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