1,721,408 research outputs found
Crystallization conditions of micas in oxidized igneous systems
No full textThe Catalão II and Catalão I carbonatite complexes are Cretaceous intrusions in the northwestern part of the Alto Paranaíba Igneous Province, central Brazil, and contain various trioctahedral micas. Drill-hole sampling and mineralogical and geochemical data suggest the existence of different types of cumulate rocks as carbonatites (calcio- and ferrocarbonatites in Catalão II; magnesiocarbonatites in Catalão I), magnetitites, apatitites, and phlogopitites. In Catalão II complex the presence of ultra-mafic lamprophyres (phlogopite-picrites) and fenites (syenites and clinopyroxenites) are identified. Phlogopite, Fe3+-rich phlogopite, and tetraferriphlogopite are ubiquitous, with marked and variable pleochroism. In the Catalão II, micas from magnetitites, apatitites, and calciocarbonatites are close in composition to the tetraferriphlogopite end-member. The Mg/(Mg+[VI]Fetot) average value is 0.959 for micas from magnetitites, 0.878 for micas from apatitites, and 0.875 for micas from calciocarbonatites, suggesting an enrichment of octahedral iron in crystals from calciocarbonatites. The trioctahedral micas from the fenites are intermediate in composition between phlogopite and tetraferriphlogopite, with 0.227 ≤ [IV]Fe ≤ 0.291 apfu. Micas of phlogopitites, ferrocarbonatites, and phlogopite-picrites show a significant variation in [IV]Fe, [IV]Al, [VI]Mg, and [VI]Fe contents, suggesting the existence of different mica populations. In the Catalão I magnetitites micas show a quite constant Mg content but marked differences in [IV]Fe3+ and [IV]Al content, so there are [IV]Fe3+-bearing phlogopite and tetrafer-riphlogopite. The micas from Catalão I apatitites have variable [IV]Fe3+, [IV]Al, and Mg contents and are mainly tetraferriphlogopite with a minor phlogopite population. Trioctahedral micas from Catalão I magnesiocarbonatites contain crystals close to tetraferriphlogopite with [IV]Fe3+ and a limited variation in Mg content. In these complexes, heterovalent octahedral substitutions are mainly related to Ti4+ and, only in a few samples, to Fe3+. The primary mechanism regulating Ti uptake into the mica structure is the Ti-oxy [[VI]Ti4+[VI](Mg,Fe)2-+1(OH)--2O22-] substitution. Crystal structural analysis shows that all mica crystals are 1M polytypes with the expected space group C2/m. The nearly equal size and mean electron count between M1 and M2 octahedral sites suggest a disorder of octahedral cations between these two sites. The low Al and the high Fe3+ content in the tetrahedral site of these micas, as well as the high (OH)- content, reflects the general enrichment in FeO and H2O and the peralkaline nature of magma from which Catalão I and Catalão II micas crystallized. Micas strongly enriched in Fe3+ and poor in Ti and Al, are used, for the first time, as indicators of crystallization temperature using published geothermometers. Temperatures range between ∼800 and 558°C for the Catalão II cumulate rocks, in high oxygen fugacity conditions, mainly over the HM condition. In contrast, the variability in temperature (703-631 and 1050-952°C) for Catalão II phlogopite-picrites is consistent with mica crystallization in an HM-NiNiO environment. The calculated temperatures for Catalão I cumulate rocks (742-542°C for magnesiocarbonatites, 923-540°C for magnetitites, and 679-550°C for apatitites) are quite similar with those of Catalão II rocks, but they generally show higher oxygen fugacity conditions (over HM condition)
Shear Capacity Model with Variable Orientation of Concrete Stress Field for RC Beams Strengthened by FRP with Different Inclinations
Full text linkA design-oriented analytical model able to evaluate the shear capacity of reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) sheets or strips oriented in any direction is proposed. The formulation of the model is based on the variable-inclination stress-field approach, aiming to extend the provisions of current European standards to beams strengthened in shear using FRP. The main novelty of the model lies in taking into account the possible different inclination of steel stirrup and FRP reinforcement in determining the orientation of a compressed concrete stress field, and in shear strength evaluation, overcoming the approximation of the known models with variable inclination of the concrete strut in the assessment of concrete strut capacity, in which the value that has to be assigned to the shear reinforcement direction is not defined, that is, either that of the steel stirrup or the external FRP reinforcement. The proposed model is able to take into account different steel stirrup and external FRP shear reinforcement orientation in assessing the reduction of the steel transverse reinforcement efficiency due to the brittle failure of the composite and also as a function of the effective composite to yielding steel strain ratio. Moreover, regarding the former aspect, a simplified approximate procedure is proposed for solving the drawbacks related to verifying compressed concrete strength in the suggested method of application of code models for RC beams strengthened by means of FRP reinforcement inclined with a different slope from the pre-existing steel stirrup. Complete and U-shaped schemes are considered. The effectiveness of the proposed model adopting different relations for assessment of the FRP effective strains proposed in the literature is investigated, differentiating them by shape of the cross section and by the possible presence of fiber-anchoring devices. The shear capacity predicted by the model and those obtained using international codes and literature models are compared against the experimental results, proving that the proposed model is the most effective in predicting the shear strength when considering specimens having steel stirrups and FRP shear reinforcement arranged with different inclinations
Development of highly oriented porous structures by PCL/PEO co-continuous blends
No full textA strategy for the preparation of porous structures for tissue engineering by using co-extrusion was proposed. Polycaprolactone Is blended with polyethylene oxide by using a twin-screw extruder to form a two-phase material with micron-sized domains. The selective dissolution of the water soluble Polyethylene oxide) allows reaching a porous material. Current work is aimed to define a methodology which enables to confer a preferential orientation of pores In order to develop highly complex structural systems to apply in tissue engineering field for the regeneration of highly oriented tissues as nerves and muscle
Early Cretaceous ultramafic-alkaline-carbonatite magmatism in the Shillong Plateau-Mikir Hills, northeastern India – a synthesis
No full textA comprehensive mineralogical, geochemical and isotopic review of six ultramafic-alkaline-carbonatite magmatic intrusions of the Shillong Plateau (Sung Valley, Jasra, Swangkre-Rongjeng, and Mawpyut) and Mikir Hills (Samchampi-Samteran and Barpung) is presented here, using the published data. These intrusions emplaced ca. 115–102 Ma ago, thus are significantly younger than the tholeiitic flood basalts erupted in Rajmahal-Sylhet province (ca. 118–115 Ma). The intrusive lithologies vary from ultramafic (dunites, clinopyroxenites, melilitolites) to mafic (ijolites, gabbros sensu lato, shonkinites), to felsic (syenites, nepheline syenites) and carbonatites (mostly calcite-rich varieties). The volcanic-subvolcanic facies (lamprophyres, phonolites) are not abundant. The range of chemical compositions of the magmatic phases in the various assemblages is notable; the intrusive rocks are thus the result of crystallization of magmas from variably evolved, independent liquid-lines-of descent, generally of alkaline/strongly alkaline lineages and sodic-to-potassic in affinity. The large variations of the Sr–Nd isotopic ratios of the silicate intrusive rocks (sensu lato) suggest a role of shallow-level crustal contamination during their formation. The carbonatites of the Sung Valley and Samchampi-Samteran have different isotope ratios than the associated silicate rocks, have some isotopic affinity with the Group I tholeiitic basalts of Rajmahal Traps and have an ultimate genesis in a carbonate-bearing lithospheric mantle
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
Raw materials for ancient ceramic productions from Campania region: provenance studies by means of Sr-Nd isotopes
No full textWhen archaeometric studies on archaeological ceramics are performed, one of the most important questions
asked by archaeologists is the provenance of pottery. This is usually performed by comparing mineropetrographic
and chemical composition of ceramics with that of local raw materials (clays, temper), production
indicators and appropriate reference groups. Nevertheless, the commonly-used analytical techniques (e.g. OM,
SEM-EDS, XRF, ICP-MS) may not always be helpful for the determination of provenance. Indeed, processing
of raw materials, such as tempering or levigation, can significantly modify their original chemical composition,
sometimes leading to an ineffective identification of raw material resources. For this reason, a pioneering
analytical approach has been recently applied by measuring the Sr and Nd isotopic signature.
Isotope analysis has largely used in archaeological sciences to date objects and identify their provenance,
making it also a useful tool for the determination of provenance of ceramic vessels (De Bonis et al., 2018 and
references therein). For this study, 87Sr/86Sr and 143Nd/144Nd isotope ratios were measured on archaeological
pottery from Campania and raw materials (clays and volcanic temper) exploited in antiquity for producing
ceramics. The analyses were focused on samples from both the Bay of Naples and Southern Campania. The
isotope signatures allowed us to better discriminate among different productions and find a strong relationship
between the archaeological pottery and the geological sources of raw materials.
In order to validate the method, Sr-Nd isotope ratios were also measured for the first time on experimental
ceramic materials that replicate archaeological pottery (De Bonis et al., 2018). It was interesting to note that
synthetic mixtures used for the ceramic replicas plot exactly on the theoretical mixing curve between the
clay and volcanic temper end-members. This suggests that the artificial manipulation of raw materials (firing,
levigation, tempering) induces no significant variations to the Sr-Nd isotope fingerprint, which strictly depends
on the geochemical affinity of the raw materials. Thus, isotopic analysis can be considered as an effective
and robust method that could complement the common multi-analytical approach in order to more precisely
constrain potential geological sources for ceramic materials and pottery provenance.
De Bonis, A., Arienzo I., D’Antonio, M., Franciosi, L., Germinario, C., Grifa, C., Guarino, V., Langella, A. & Morra, V.
(2018): Sr-Nd isotopic fingerprint as a tool for ceramic provenance: application on raw materials, ceramic replicas and
ancient pottery. J. Archaeol. Sci., 94, 51-59
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
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