1,721,035 research outputs found
NOBLE GAS INVENTORY OF TRANSANTARCTIC MOUNTAIN MICROMETEORITES: INSIGHTS INTO THEIR PROVENANCE.
No full textIntroduction: : A variety of processes have been considered possibly contributing volatiles, including the noble
gases, to the terrestrial planets (e.g., [1-3]). Special consideration has been given to the concept of accretion of volatilerich
materials by the forming planets. This might include infalling extraterrestrial material of various sizes, i.e. from
planetesimals down to dust, and could include material from the outer asteroid belt, as well as material of cometary
origin. Currently, the dominant source of extraterrestrial material accreted by the Earth is represented by micrometeorites
(MMs) with sizes mostly in the 100-400 μm range [3, 4]), and according to [3] accretion of early micrometeorites
may have played a major role in the formation of the terrestrial atmosphere and oceans. We have therefore set out
to investigate in more detail the complete inventory of noble gases in MMs. Here we summarize some of the results
we obtained on MMs collected in micrometeorite traps on the tops of the Transantarctic Mountains [5].
Trapped noble gases: Concentrations in “unmelted”
MMs, in the size range ~400-1000 μm, are
compared to those in CM meteorites (exemplified by
CM2 Maribo) in Figure 1. While He has been largely
lost, the abundance of Ne often exceeds that in CMs,
because of higher abundances of trapped solar wind Ne.
Ar, Kr, Xe are somewhat lower and quite variable. This
is in line with our mineralogical observations on separate
pieces of the analyzed MMs that mostly show similarities
to ordinary chondrites of various types rather
than CMs - contrary to the situation for recently fallen
MMs recovered from ice and snow of Central Antarctica
[6, 7]. Note, though, that uncertainty is induced by
a) the fact that the MMs are often not homogeneous in
composition and b) the complex interaction during passage
through the terrestrial atmosphere. Among others,
we found in several cases (two scoriaceous, one unmelted)
Kr and Xe showing the signature of isotopically
fractionated air with the heavier isotopes enriched [8].
abundance relative to Maribo 2
10-3
10-2
10-1
100
101
45b unmelted
45c unmelted
45c.29
4He 20Ne 36Ar 84Kr 132Xe
Fig. 1. Trapped noble gas abundances in nominally unmelted
TAM MMs, normalized to CM Maribo [9]. Two fragments of
the special MM 45c29 are shown. In addition, for an aliquout
of one of the plotted MMs as well as for one additional “unmelted”
MM abundances were below detection limit.
Cosmic ray exposure: Neon is generally dominated by fractionated solar wind, but cosmogenic contributions are
apparent in a number of cases. Cosmogenic noble gases can be used to infer cosmic ray exposure and (due to the
Poynting-Robertson effect) the distance from the sun where particles (or dusts) began their journey to the inner Solar
System [10]. In addition the isotopic composition of cosmogenic Ne contains information about irradiation conditions.
From a comparison with model predictions [10] it follows that data for the MMs with the clearest cosmogenic signature
are incompatible with irradiation by galactic cosmic rays (GCR) as small particles. Precursors of MMs could have
been exposed to GCR as part of a larger body or to solar cosmic rays (SCR) as small particles. In the latter case a SCR
energy spectrum is required that is softer than the one favored in [10].
45c29: This MM is characterized by several unique features: a) high abundances not only of cosmogenic Ne but
also cosmogenic Ar, with extremely low cosmogenic 21Ne/38Ar in one analyzed aliquot, but less so in a second specimen,
attesting to an inhomogeneous composition; b) evidence for radiogenic 129Xe and fission Xe from 244Pu. These
properties are similar to, but not identical in all details, to achondrites or Ca-Al-rich inclusions (CAIs). Since for MMs
derived from beyond ~ 4 a.u. the GCR contribution should exceed that from SCR [10], the high abundance of cosmogenic
Ne is difficult to reconcile with its isotopic composition
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
The composition of salt-rich ice grains emitted by Enceladus' cryo-volcanic plume and implications for the subsurface ocean
Full text linkSalt-rich icy particles within Saturn’s E-ring are thought to originate from frozen aerosolized droplets of the salty seawater of Enceladus’ subsurface ocean. They are ejected into space, through fractures in the moon’s south polar region, within a plume of gas and ice particles. Some of these icy particles can escape the gravity of Enceladus thanks to their high velocities, and become E-ring particles, which typically have relatively young (no more than 200 years) ages. Therefore, it is believed that the salt-rich grains reflect the composition of the subsurface ocean water.
The in situ mass spectra of E-ring and plume icy particles, produced by the Cosmic Dust Analyzer (CDA) impact ionization mass spectrometer onboard the Cassini spacecraft, reveal significant compositional diversity within the salt-rich population. Understanding the compositions of dissolved substance, including salt, silica, and organics, within the grains, and thus in the ocean, can provide crucial constraints for geochemical models of Enceladus’ subsurface ocean environment.
The research presented in this thesis investigates the compositional diversity of the in situ mass spectra and hence the salt-rich icy particles and attempts to quantify the variations in grain composition with the aid of analogue mass spectra generated in the laboratory.
In this work, the in situ mass spectra and thus the salt-rich icy particles are classified into various compositional groups and subtypes. The major subtype distributions of E-ring spectra/particles with respect to distance to Saturn, impact speed and size have been studied and the contrast between the E-ring population and plume population examined. The major findings are: The `sodium-rich and potassium-poor' spectra (and hence icy particles) are the majority among both E-ring and plume salt-rich populations, while `potassium-rich and sodium-poor' spectra and `both sodium and potassium-rich' spectra are rare. Carbonate and chloride-containing spectra are mutually exclusive in most cases. The `sodium-rich and potassium-poor' spectra (and hence icy particles) are further classified into Subtypes A, B, H, C, D, E and L according to the presence and relative amplitudes of carbonate and chloride related peaks. Among them Subtypes A, B, C, D and L are the majorities in E-ring spectra. A part of ice particles producing Subtype A and Subtype L spectra at lower impact speed could produce Subtype B spectra at higher impact speed. While abundances of the major sodium subtypes are comparable in the E-ring salt-rich populations, the ultra carbonate-rich subtype, which is named as Subtype A, spectra are much more frequent than the spectra of other subtypes in the plume salt-rich population, which implies that the majority of the ultra carbonate rich (Subtype A) ice particles do not have enough energy to escape from the gravity of Enceladus and reach the E-ring or that the E-ring grains are older and rapidly lose their carbonate signature. The spatial distribution of the subtypes and relative peak amplitudes implies the carbonate and chloride compounds in the ice particles are lost slowly with time. The impact speed distributions of the subtypes and relative peak amplitudes for the spectra of E-ring salt-rich ice particles imply higher impact speeds tend to break up carbonate molecules and thus lower the amplitudes of carbonate related peaks.
To quantify the grains' compositions, a Laser Induced Liquid Beam Ion Desorption (LILBID) technique was used to desorb and ionize a wide range of Enceladean ocean-like solutions containing dissolved salts. The resulting ions were then measured by a reflectron-type time of flight mass spectrometer. Since the laser desorption mechanism simulates the ice grain impact process occurring on the CDA target, spectra produced in the laboratory from a large range of well-characterized salt solutions can be used to determine the CDA-applicable spectral appearances of substances within the ice grains emitted from Enceladus’ ocean.
Firstly, the composition parameter space, with NaOH, NaCl, and Na2CO3 as endmembers, for the four major subtypes of salt-rich ice particle were explored via spectra mimicking. After this, I reconstructed the mass spectra from chloride-rich and carbonate-rich Enceladus ocean analogues, into which trace concentrations of a wide range of geochemically-relevant salts, silica and organics were been dissolved, to evaluate their detection limits for CDA impact ionization mass spectra of the frozen ocean droplets. ocean droplets.Es wird angenommen, dass die salzhaltigen Eispartikel im E-Ring des Saturns von gefrorenen aerosolisierten Tröpfchen des salzigen unterirdischen Ozeanwassers von Enceladus stammen. Sie werden in einem Plume aus Gas und Eispartikeln durch Spalten in der südlichen Polarregion des Mondes in den Weltraum geschleudert. Aufgrund ihrer Geschwindigkeit können einige dieser eisigen Partikel Enceladus‘ Schwerkraft entkommen und werden zu E-Ring-Teilchen, die typischerweise ein relativ junges Alter (nicht mehr als 200 Jahre) haben. Daher wird angenommen, dass die salzreichen Teilchen die Zusammensetzung des unterirdischen Ozeans Wasser widerspiegeln.
Die in-situ-Massenspektren von E-Ring- und Plume-Eispartikeln, die mit dem Cosmic Dust Analyzer (CDA), einem Einschlagsionisations-Massenspektrometer an Bord der Cassini-Raumsonde erstellt wurden, zeigen eine erhebliche Vielfalt in der Zusammensetzung der salzhaltigen Partikel. Das Verständnis der Zusammensetzungen der in den Eisteilchen (und damit im Ozean) gelösten Substanzen, einschließlich Salze, Siliziumdioxid und organische Komponenten, kann entscheidende Hinweise für geochemische Ozeanmodelle für Enceladus liefern.
Diese Arbeit untersucht die Vielfältigkeit der in situ Massenspektren der salzreichen Eispartikel und versucht, die Variationen in der Zusammensetzung der Eispartikel mit Hilfe von Analogexperimenten im Labor zu quantifizieren.
Die in situ Massenspektren und damit die salzreichen Eispartikel werden anhand ihrer Zusammensetzung in verschiedene Gruppen und Subtypen eingeteilt. Die Verteilung der wichtigsten Subtypen der E-Ring-Spektren/Partikel hinsichtlich deren Abstand zu Saturn, Einschlagsgeschwindigkeit und Größe wurden untersucht. Außerdem wurde der Unterschied zwischen der E-Ring- und der Plume-Population untersucht. Die wichtigsten Ergebnisse sind: Die „natriumreichen und kaliumarmen“ Spektren (und damit Eisteilchen) machen den größten Teil sowohl der E-Ring- als auch der Plume-Population aus, während sowohl die „kaliumreichen und natriumarmen“ Spektren als auch die „natriumreichen und kaliumreichen“ Spektren selten sind. Carbonat- und chloridhaltige Spektren schließen sich in den meisten Fällen gegenseitig aus. Die „natriumreichen und kaliumarmen“ Spektren (und damit Eisteilchen) werden basierend auf den relativen Amplituden von carbonat- und chloridbezogenen Peaks weiter in die Untertypen A, B, H, C, D, E und L unterteilt. Von diesen Untertypen sind A, B, C, D und L die häufigstens im E-Ring. Ein Teil der Eispartikel, die Subtyp A und Subtyp L Spektren bei niedrigen Einschlagsgeschwindigkeiten erzeugt, könnte bei höheren Einschlagsgeschwindigkeiten Spektren des Subtyps B erzeugen. Die Häufigkeiten der wichtigsten Natrium-Subtypen innerhalb der salzreichen E-Ring-Populationen sind vergleichbar. Die Spektren des ultrakarbonatreichen Subtyps A sind viel häufiger als die Spektren der anderen Subtypen in der salzreichen Population des Plumes zu finden, was bedeutet, dass die Energie der Mehrheit der ultrakarbonatreichen reichen (Subtyp A) Eispartikel nicht ausreicht, um der Schwerkraft von Enceladus zu entkommen, sodass sie den E-Ring erreichen könnten. Möglich ist auch, dass die E-Ring-Teilchen älter sind und rasch ihre karbonatsignatur verlieren. Die räumliche Verteilung der Subtypen und der relativen Peakamplituden legt nahe, dass die Karbonat- und Chlorid-Komponenten in den Eispartikeln mit der Zeit verloren gehen. Sowohl die Verteilung der Einschlagsgeschwindigkeiten der Subtypen als auch die der relativen Peakamplituden in den Spektren der salzreichen E-Ring Eispartikel implizieren, dass höhere Einschlagsgeschwindigkeiten tendenziell die Karbonatmoleküle aufbrechen und somit die Amplituden der karbonatbezogenen Peaks verringern.
Um die Zusammensetzung der Eisteilchen zu quantifizieren, wurde eine laserinduzierte Flüssigstrahl-Desorptions (LILBID) Methode verwendet, um ein breites Spektrum von Enceladusozean-ähnlichen Lösungen zu desorbieren und zu ionisieren. Die enstandenen Ionen wurden mit einem Reflektron-Flugzeit-Massenspektrometer gemessen. Da der Laser-Desorptionsmechanismus den Einschlag der Eispartikel auf das CDA-Instrument simuliert, können im Labor erzeugte Massenspektren von einer großen Anzahl gut charakterisierter Salzlösungen verwendet werden, um deren spektrales Erscheinungsbild in CDA-Massenspektren zu bestimmen.
Zunächst wurde der Parameterraum (NaOH, NaCl und Na2CO3 als Endglieder) für die vier bedeutendsten Untertypen von salzreichen Eispartikeln untersucht, indem die Massenspektren dieser Untertypen im Labor nachgestellt wurden. Danach rekonstruierte ich die Massenspektren von chloridreichen und karbonatreichen Enceladus-Ozean-Analoga, in denen Spurenkonzentrationen von einer Vielzahl von geochemisch relevanten Salzen, Siliziumdioxid und organischen Substanzen gelöst wurden, um deren Nachweisgrenzen für die CDA-Einschlagsionisationsmassenspektren der gefrorenen Ozeantröpfchen zu bestimmen
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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