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Nanodiamonds
No full textNanodiamonds were discovered in the course of the search for the carrier of the exotic noble gas component HL, strongly enriched in both the heavy (H) and light (L) isotopes of Xe, with correlated features in other noble gas elements. Additional noble gas components carried by the nanodiamonds are P3 and P6. The nanodiamonds are isolated by a series of chemical and physical separation steps, the application of which led to the discovery of additional types of grains of presolar origin, which are described in other chapters of this book. Unlike these, the isotopic compositions of nanodiamonds, with an average grain diameter of 2.5–3 nm, cannot be studied in detail individually, hence what fraction of them is truly presolar, is currently unknown. The composition of macroscopic samples of nanodiamonds shows C and N isotopic ratios that are within the range observed in Solar System materials, hence links to stellar sources are provided by trace elements like Xe only. The enhancements of the light isotopes in the abundant Xe-HL are probably produced by a variant of the p-process, and the enhancements in the heavy isotopes by a variant of the r-process or a neutron burst, thus pointing to a supernova. A very small fraction, so far observed in nanodiamonds from only one meteorite, shows an enrichment of s-process Xe tying it to an AGB star source. The P3 component is isotopically close to normal, while P6 is ill-defined. The HL and P3 noble gases were most likely introduced by ion implantation in separate events. Small variations in C and N isotopic compositions point to the existence of subpopulations that can be linked to the noble gas components P3 and HL. Microstructural investigations show that the vast majority of the nanodiamonds formed by a CVD-like process, not by shock transformation
Author Correction: Contribution of Ryugu-like material to Earth’s volatile inventory by Cu and Zn isotopic analysis
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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
Ryugu’s nucleosynthetic heritage from the outskirts of the Solar System
No full textLittle is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here, we show that samples returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the Main Belt. In this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune.Asteroid Ryugu and Ivuna-type carbonaceous meteorites may have originated from the outskirts of the Solar System
Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites
No full textCarbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do
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
The Magnesium Isotope Composition of Samples Returned from Asteroid Ryugu
No full textAbstract The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ 26 Mg* and μ 25 Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ 25 Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ 25 Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg ( μ 25 Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ 26 Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ 26 Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26 Al given their respective 27 Al/ 24 Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26 Al/ 27 Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.EC ∣ ERC ∣ HORIZON EUROPE European Research CouncilCarlsbergfonde
Contribution of Ryugu-like material to Earth’s volatile inventory by Cu and Zn isotopic analysis
No full textCarbonate record of temporal change in oxygen fugacity and gaseous species in asteroid Ryugu
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