1,720,999 research outputs found
Transport of carbon and hydrogen in subducted oceanic crust: an experimental study to 5 GPa
No full textCarbon and hydrogen residence time in the Earth''s interior is controlled by complex phase equilibria attained
in the subduction zone environment. Carbonic fluid/melts are highly mobile, whereas graphite–diamond are
refractory and sluggishly participate in subsolidus reactions; on the contrary carbonates although refractory
are extremely reactive. Inclusions of diamond/graphite+carbonates +hydrates in both orogenic and
subcratonic mantle remnants reveal that the fates of C and H are intimately related.
Experiments were carried out on an altered MORB bulk composition at P from 2.2 to 5.0 GPa and T from
680 °C to 800 °C, in the presence of a fluid at variable C–O–H ratios and amounts. The role of variable redox
conditions was explored buffering fH2 at NNO and HM equilibria using a double capsule technique.
Amphibole breaks down at 2.5–2.6 GPa, epidote persists to 2.7 GPa, 730 °C and talc to 3.3 GPa, 800 °C.
Graphite is ubiquitous above 2.0 GPa at both hydrogen fugacities. At PN2.0 GPa and fH2 buffered by NNO,
dolomite was recovered at 3.0 GPa, 730 °C only, in an experiment with large amount of volatiles added. On
the contrary, at fH2 buffered by HM, carbonate phase fields get wider with pressure: aragonite and/or
dolomite are stable up to 2.4 GPa and at higher pressure they are replaced by coexisting magnesite and
dolomite. Mg–calcite forms at 4.6–5.0 GPa, 800 °C. Unexpectedly, lawsonite was found to coexist with
magnesite at temperatures as high as 700 °C at 3.3 GPa, and 730 °C at 4.2 GPa, revealing a thermal stability in
C–O–H bearing systems exceeding by more than 30 °C that found in mafic assemblages in the presence of
hydrous species only. Chemographic analysis reveals that pressure–temperature stability of lawsonite in
basaltic compositions is promoted by CO2 addition and by the oceanic alteration processes.
In C–O–H bearing systems, complex mass-balance relations govern the partitioning of volatiles between
fluid, hydrates, carbonates, and graphite/diamond at fixed fH2. In natural systems, the relative amounts of
ferric/ferrous iron in garnet and clinopyroxene versus C/carbonate control fluid speciation. The potential
production of C–O–H fluid mixtures is evaluated and a heterogeneous oxidation of the subducting
lithosphere is suggested as a source for distinct fluid populations. Upon mixing, these fluids promote carbon
precipitation
The world in a river? A preliminary analysis of the 16S rDNA variability of Tubifex species (Clitellata: Tubificidae) from the Lambro River
No full textTubifex tubifex Müller, 1774 is a cosmopolitan freshwater tubificid widely used as a model in ecotoxicology,
population dynamics and developmental biology. It is traditionally recognized as a polytypic species and in Lambro River (Milano, Northern Italy) it occurs in two of the three recognized forms, named ‘‘tubifex”
and ‘‘blanchardi”, alternatively considered as ecological forms or distinct species. To investigate the genetic differentiation of the populations occurring in the Lambro River we sequenced a fragment of the
16S rDNA mitochondrial gene. T. blanchardi, characterized by a low genetic diversity, was genetically segregated from the other sympatric T. tubifex. The ancestral state reconstruction was used to define the
morphological traits that support its distinctness. On the contrary, the other T. tubifex from the Lambro community, although morphologically indistinguishable, revealed an astonishing degree of genetic variability,
both between and within the three identified clades that proved to be genetically isolated. Using samples from the mixed Lambro River community and from other countries around the world we present
an overview of the species complex’ 16S rDNA variability. Our results show that the genetic variability did not sensibly increase widening the data set, suggesting that the Lambro River populations meet
the species’ worldwide genetic variability
New data on amphibians and reptiles of the Northern Areas of Pakistan : distribution, genetic variability and conservation issues
No full textThe Northern Areas of Pakistan are at the boundary between the Paleartic and the Oriental biogeographical realm. This mountainous region is at the junction between major mountain ranges, has huge altitudinal and environmental gradients, and is the focus of efforts for biodiversity conservation. However, the amphibians and reptiles of this area remain poorly known. We used multiple approaches to describe species distribution and ecology, to perform a preliminary analysis of genetic diversity of toads, and to assess the occurrence of Batrachochytrium dendrobatidis, a pathogen largely responsible of global amphibian decline. We observed seven species of amphibians and reptiles: Bufo pseudoraddei baturae, Bufo latastii, Scutiger cf. nyingchiensis, Altiphylax stoliczkai, Laudakia himalayana, L. pakistanica and Varanus bengalensis; we describe the habitat and distribution of these species. In the case of L. himalayana, we observed a bimodal pattern of diurnal activity, and we report new data on the altitudinal range of this agamid. Sequences of a fragment of mitochondrial 16S rDNA from multiple populations of B. pseudraddei baturae show low genetic diversity among individual of this species. Conversely, we observed strong genetic substructuring among populations of B. latastii living in different valleys. A PCR-based analysis did not reveal the presence of B. dendrobatidis in any of the amphibians investigated. Distribution data show that amphibians and reptiles are limited to relatively low elevations; these areas suffer the strongest human impact, and might be overlooked by future conservation plans for the area, making the future of these organisms at risk
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
Step height oscillations during layer-by-layer growth of Pb on Ge(001)
No full textHeteroepitaxial growth of Pb on the Ge(001) surface has been studied by He atom scattering. For low substrate temperatures, Pb is found to grow layer by layer with (111) orientation. A detailed analysis of the specular peak profile as a function of the He wave vector reveals that the step height of the growing monatomic terraces oscillates with the him thickness. This variation, initially as large as +/-15% around the value of the Pb(Ill) bulk interlayer spacing, gradually dampens out after the deposition of a dozen monolayers. This is direct evidence of quantum size effects affecting the interlayer distance of a growing metal film
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