1,720,974 research outputs found
From subducted organic matter to COH fluids: an experimental investigation on the redox dissolution of carbonaceous materials
Full text linkSubducted organic matter plays a key role in the production of COH fluids and volcanic arc gaseous emissions. Assessing how its intrinsic heterogeneity affects its redox dissolution is fundamental to develop more accurate models of the deep organic carbon cycle. To this purpose, we experimentally
investigated at 550 °C, 1 GPa and fO2 buffered from ΔFMQ ≈+4 to −7 the solubility of synthetic analogues of carbonaceous material (CM) characterized by peculiar structural, textural and compositional features, i.e., graphite (crystalline C(sp2); O <1 at%), mesoporous carbon (poorly ordered porous C(sp2); O <1 at%; oxygenated functional groups, OFGs, ~2%), glass-like and Vulcan® carbon (disordered sp2-rich C; C(sp3) <30 at%; up to ~8 at% O; OFGs <30 at%), graphite oxide (partly ordered C(sp3); C(sp2) <2 at%; O ~31 at%; OFGs ~41 at%). Graphite and mesoporous carbon are quite inert (CMdissolved <0.4%), glass-like and Vulcan® carbon are more soluble at extreme redox
conditions (CMdissolved ~1% at ΔFMQ ≈+4 and >1% at ΔFMQ ≈–7), graphite oxide reacts extensively at all redox conditions (CMdissolved >2%). In the fluid CO2 and CO are the dominant volatile carbon species at ΔFMQ ≳–5; CH4 prevails at ΔFMQ ≈−7 in all the runs except that with graphite oxide. Low
crystallinity, high content of C(sp3), O and OFGs appear to increase CM solubility. In particular, a high content of O heteroatoms and OFGs promotes CO2 release, while the formation of H- and O-bearing surface complexes probably accompanies the production of CO as reaction intermediate. Hydrogen adsorption on active sites seems to reduce graphite and mesoporous carbon reactivity at ΔFMQ ≈−5 and −7; a similar process likely hinders methane formation in the runs at ΔFMQ ≈−5, where a pure CH4 fluid would be expected from thermodynamics. These results can indicate that immature CM (poorly crystalline, C(sp3)- and O-rich) is more prone to dissolution at the onset of dehydration reaction in forearcs and may give a fundamental contribution to the organic carbon flux. Moreover, the high stability of some H- and O-bearing functional groups may be associated with a previously neglected flux of hydrogen and oxygen associated with CM subduction
A novel approach for quantitative analysis of S-bearing volatile species generated from HP-HT experiments
No full textA novel approach for quantitative analysis of S-bearing volatile species generated from HP-HT experiments
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
A reliable analytical procedure to determine the carbon isotopic signature of CO2-bearing COH fluids generated in petrological experiments
Full text linkThe ratio of stable carbon isotopes, δ13C, serves as a fundamental tracer for geological processes.
Experiments aiming to replicate isotopic exchange between carbon reservoirs encounter significant analytical
challenges due to the limited sample size and issues related to sampling, particularly when dealing with volatile
species. Here we present a novel methodology that integrates a capsule-piercing device, a quadrupole mass spec-
trometer (QMS), and isotopic ratio mass spectrometry (IRMS) to measure the CO2 concentration and natural-like
δ13C ratio of CO2 in the volatile COH phase generated in petrological experiments. To validate the technique,
we first analyze the COH fluid resulting from the thermal decomposition of 1 mg of anhydrous oxalic acid. The
optimal values of the carrier gas flow in the QMS, sampling times, and chromatography column temperature for
IRMS are determined. The high degree of similarity, within acceptable errors, observed in both compositional
and isotopic analyses indicates a robust reproducibility, minimally affected by contamination and fractiona-
tion effects during sampling. We also show that this methodology can be applied for estimating the δ13C of
CO2 produced from high-pressure, high-temperature, redox-buffered piston–cylinder experiments. This offers a
multitude of opportunities in designing experiments focused on determining isotopic fractionation models for
geological processes that involve, but are not restricted to, CO2-bearing COH fluids
What controls the geochemical variability of massive sulfide deposits on mid-ocean ridges? Indications from multivariate statistical analysis
No full textExperimental dissolution of carbonaceous materials in water at 1 GPa and 550°C: Assessing the role of carbon forms and redox state on COH fluid production and composition during forearc subduction of organic matter
Full text linkBiogenic carbonaceous material (CM) is the main carrier of organic carbon in the
subduction zone and contributes to COH fluid production and volcanic arc gaseous
emissions. Here we investigated the effect of the structural, textural and chemical
heterogeneity of CM on its reactivity and redox dissolution by conducting short-lived
(1 h) experiments, where synthetic analogues of CM (ordered graphite, graphite oxide
(GO), mesoporous carbon (MC), Vulcan ®
carbon (VC) and glass-like carbon (GC)), are
reacted with water at P = 1 GPa and T = 550° C—conditions typical of a warm forearc
subduction—and fO2 buffered from ΔFMQ ≈ +4 to −7. We show that the amount of
dissolved CM (CMdissolved) and the proportion of volatile carbon species (C volatile) in
the fluid is related both to the structure and the peculiar surficial properties of the
carbon forms, such as carbon sp2-and sp 3-hybridization, amount of oxygen
heteroatoms, presence of oxygenated functional groups (OFGs) and of active
sites. MC and graphite (C(sp 2) > 93 at%, O < 1 at%, OFGs < 2.3 at%, high
proportion of active sites) are relatively inert (CMdissolved < .4 mol%) but the
former reacts more extensively at extreme redox conditions (producing CO 2 +
CO and CO 2 + CH4 Cvolatile mixtures at ΔFMQ ≈ +4 and −7, respectively), while the
latter has a maximum of C volatile production (CO 2 + CH 4) at ΔFMQ ≈0, which is not
observed in a 10-day long run; partly-ordered GO (C(sp3) > 98 at%, O ~31 at%, OFGs
~41 at%) is the most reactive material at all redox conditions (CM dissolved > 2.6 mol%)
and produces CO 2 as the dominant Cvolatile species; disordered GC and VC (C(sp3) <
30 at%, O < 8 at%, OFGs < 30 at%) are more reactive at ΔFMQ ≈ +4 (CM dissolved ~1 mol
%) and ΔFMQ ≈ –7 (CM dissolved > 1 mol%), where C volatile is dominantly CO2 and CH 4,
respectively. Besides the significant deviations from thermodynamically predicted
graphite-saturated COH fluid composition and speciation, our results suggests that:
1) immature CM (disordered, rich in C(sp 3), O, OFGs) is preferentially dissolved under
high fluid fluxes and may buffer fluids to rather oxidizing conditions; 2) a descending
flux of oxygen (and hydrogen) bond to CM may exist
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
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