1,721,012 research outputs found
Polyphase inclusions in garnet pyroxenites from Sulu (China) as carriers of seawater at ultrahigh pressure
No full textUnravelling processes of fluid-mediated element exchange between slab lithologies and the mantle wedge is of primary importance in understanding element mobility in subduction zones. Several studies have addressed element transfer related to fluid release during prograde metamorphism in subduction zones [1-4]. Nevertheless, detailed studies documenting interactions between felsic, mafic and ultramafic rocks at ultrahigh-pressure (UHP) are still scarce [5]. For this reason, UHP metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones.
We present preliminary results of Ca-rich garnet–clinopyroxenites from Suolushu, occurring as layers in a large serpentinite body at Hujialin, Rizhao County, in the Sulu UHP metamorphic terrane (eastern China). Both clinopyroxenites and hosting serpentinites are intercalated with coesite-eclogites and hosted by coesite-bearing gneiss. Similar garnet–clinpyroxene layers from Hujialin have been studied by [6] and interpreted as cumulates crystallised from a hydrous, subduction related magma at ~ 1 GPa and 1000 °C. They were subjected to minor Ca enrichment coeval with serpentinisation of the host ultramafic rocks and then subducted at UHP (4.8 ±0.6 GPa and 750 ±50 °C). Ca-rich garnet–clinopyroxenites are composed of centimeter-sized garnet porphyroblasts in a matrix of fine-grained green diopside, opaque minerals associated with green spinel, and garnet. Garnet porphyroblasts include rounded clinopyroxene, opaque minerals, and/or spinel grains. Aggregates of magnetite and spinel are abundant in some samples. Peak porphyroblastic garnets preserve primary polyphase inclusions in their cores, consisting of amphibole(s), chlorite, pyroxene, micas and spinel. We studied these inclusions with the Transmission Electron Microscope at the University of Milano. They show an inner part formed by amphibole and clinopyroxene surrounded by Al rich Mg-silicates. Amphibole and pyroxene grow coherently by sharing the [001] direction, the one parallel to the tetrahedral chains. At the grain boundary between amphiboles and pyroxene, or amphiboles and Al rich Mg silicates, smaller amphibole grains extremely enriched in both Cl (up to 8 at.%) and Sr (up to 1.5 at.%) occasionally occur. Such Cl-amphiboles grow coherently with the neighbouring amphibole. The Al rich Mg-silicate phases show electron diffraction patterns with several streaking, indicating possible polytypic disorder. They exhibit periodicities of 14.1 Å, characteristic of chlorite. These phases form a rim between the inclusion precipitates and the hosting garnet, whereas a direct contact between garnet and amphibole or pyroxene have never been observed.
Serpentinites act as carriers of oceanic Cl, B, Sr, Rb, Cs, and alkalis which are recycled into variably saline fluids within the stability field of antigorite serpentine [7]. Polyphase inclusions studied in Hujalin clinopyroxenites likely derive from the interaction with the hosting serpentinites at HP-UHP and could represent a snapshot of such fluid-mediated element recycling occurring in the slab at sub-arc depths.
References. [1] Bebout, G.E., Ryan, J.G., Leeman, W.P., Bebout, A.E. (1999): Earth Planet. Sci. Lett, 171, 63–81; [2] Becker, H., Jochum, K.P., Carlson, R.W. (2000): Geology, 163, 65–99; [3] Scambelluri, M., Philippot, P. (2001): Lithos, 55, 213–227; [4] Spandler, C.J., Hermann, J., Arculus, R.J., Mavrogenes, J.A. (2003): Contrib. Mineral. Petrol., 146, 205–222; [5] Malaspina, N., Hermann, J., Scambelluri, M., Compagnoni, R. (2006): Lithos, 90, 19–42; [6] Yang, J.J. (2006): J. Petrol., 47, 965–990; [7] Scambelluri, M., Fiebig, J., Malaspina, N., Müntener, O., Pettke, T. (2004): Int. Geol. Rev., 46, 595–613
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
Functional Roles of the Hexamer Organization of Plant Glutamate Decarboxylase
No full textGlutamate decarboxylase (GAD) is a pyridoxal 5 ́-phosphate (PLP)-dependent enzyme that catalyzes the irreversible α-decarboxylation of glutamate to γ-aminobutyrate. The enzyme is widely distributed in eukaryotes and prokaryotes, although its function varies in different organisms. A unique feature of plant GAD is the presence of a calmodulin (CaM)-binding domain at its C-terminus. In plants, transient elevation of cytosolic Ca2+ in response to different types of stress is thought to be responsible for GAD activation via CaM. The crystal structure of GAD1 from Arabidopsis thaliana shows that the enzyme is a hexamer composed of trimer-of-dimers. Herein, we show that in solution GAD1 exists as a dimer/hexamer equilibrium mixture, and we estimate the dissociation constant (Kd) for the hexamer under different conditions. The association of dimers into hexamers is promoted by a number of conditions, including high protein concentrations and low pH. Notably, binding of Ca2+/CaM abolishes GAD1 oligomer dissociation by forming a stable complex in which three CaM bind to a GAD1 hexamer. The GAD1 N-terminal domain is critical for maintaining the oligomeric state, since the removal of the first 24 N-terminal residues dramatically affects the oligomerization process by producing an enzyme that exists only as a dimer. The deleted mutant retains decarboxylase activity, highlighting the dimeric nature of the basic structural unit of GAD1. Site-directed mutagenesis identified a hexamerization ‘hot spot’ centered on Arg24 in the N-terminal domain. Mutation of this critical Arg residue to Ala prevents hexamer formation in solution. Surprisingly, both the dimeric ArgAla and 1-24 mutant enzymes form a stable hexamer in the presence of Ca2+/CaM. The present data, clearly revealing that the GAD1 oligomeric state is highly responsive to a number of experimental parameters, might have functional relevance in vivo and is discussed in the light of the biphasic regulation of GAD1 activity by pH and Ca2+/CaM in plant cells
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
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