1,720,979 research outputs found
Conceptual design of a SuperConducting Energy Pipeline for LH2 and power transmission over long distances
Get PDFThe design of a single-pole MgB2 superconducting hydrogen-cooled cable for DC current transmission at low voltage (10 kV) is presented here. The cable consists of a former made of MgB2 superconducting wires, a dielectric layer and an annular region that allows for the passage of hydrogen at inlet pressures above the critical one. The cable is contained within a corrugated cryostat, insulated from the external environment. The use of MgB2 as a superconducting material allows for the operation of the cable in the range 15-27 K, which reduces the cooling requirements and increases the efficiency of the system. The hydrogen-cooled annular region, acting as a pipeline for the cryogen transport, allows at the same time the efficient cooling of the cable, while the corrugated cryostat provides additional insulation and structural support, together with a relief volume in the case of an accident. The results of this study, mainly performed with a simplified model, benchmarked against the OPENSC2 software, show that the cable is able to support DC current transmission at 10 kV, with maximum cable lengths of several tens of km for inner diameters of the cryostat > 120 mm, supporting a H 2 mass flow rate > 1 kg/s. Overall, this study demonstrates the feasibility of combining the DC current transmission at low-medium voltage by MgB 2 to the transport of liquid hydrogen, providing at the same time instantaneous storage of chemical power
Effect of disorder on the passage from bulk superconductivity to spin glass behaviour in RuSr2GdCu2O8
No full textIn this paper we analyse the structural and physical properties of rutheno-cuprate samples of the phase Ru–Gd(1212) subjected to different thermal treatments. We have observed the variations induced by these treatments by structural measurements (x-ray powder diffraction and high-resolution transmission electron microscopy) and physical measurements (dc magnetic measurements and
magnetoresistive measurements). Such variations involve both the intrinsic properties of the Ru–Gd 1212 phase
(for example the temperatures of the magnetic and superconducting ordering), and the extrinsic properties, i.e. those related to the microstructure of the samples,
such as the domain dimension, and to their granular nature. In particular, while a prolonged annealing in flowing oxygen induces an extended microstructural
homogeneity, annealing in vacuum, besides producing loss of oxygen, leads to the formation of intragranular disordered microdomains and extended planar defects.
We verify how the physical properties are dependent on the level of microstructural order that determines the passage from metallic to semiconducting behaviour and, possibly, from bulk to spin glass superconducting behaviour.
By saying ‘bulk’ superconducting behaviour we mean the behaviour commonly observed in high-Tc superconductors where, as is well known, granularity is present and intergranular and intragranular properties of the sample
may be observed: in appropriate experimental conditions it is possible to separate the two contributions to study the intrinsic properties of the material or to observe
the character of the Josephson coupling between grains (or clusters). In contrast, the ‘spin glass’ is modelled as superconducting grains weakly linked into closed
loops, where different supercurrent carrying states of nearly equal energy may install, producing, among other effects, metastable configurations. We suggest
that the microstructure is an important cause of the different behaviour of samples otherwise very similar: strong microstructural disorder decreases the domain size
inside the grains until they are comparable with the coherence length ξ (and much smaller than the penetration depth λ). In such conditions the superconducting
volume of the sample becomes smaller and smaller; granularity or weak-link behaviour becomes ubiquitously present and practically determines the physical properties in the whole phase diagram
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Thickness effect on the structure and superconductivity of Nd1.2Ba1.8Cu3Oz epitaxial films
No full textWe have studied the effect of thickness on the structure and superconductivity of Nd1.2Ba1.8Cu3Oz (NdBCO) epitaxial films deposited on SrTiO3 (100) substrates. High-quality NdBCO films were deposited by high oxygen pressure sputtering. The samples have been carefully characterized by transport measurements and x-ray diffraction using conventional and synchrotron radiation sources. Two structural transformations are observed. The first one is a crossover from the orthorhombic and twinned structure, typical of thick samples, to a pseudotetragonal phase at thickness lower than 60 unit cells. The pseudotetragonal phase exhibits peculiar x-ray diffuse scattering around the Bragg reflections, associated with nanostructured twinned domains. The second one appears at a thickness lower than 20 unit cells and is assigned to a pseudotetragonal-tetragonal transition. The transport properties are not modified at the first crossover, while a substantial decrease in T-c and in the number of holes is observed at the pseudotetragonal-tetragonal transformation. Our results suggest that the structural rearrangement and the transport properties are explained by the ordering of Cu(1)O chains. A simple model, able to explain the experimental results and capturing the essential features of the Cu(1)O chains nucleation process in the R1+xBa2-xCu3O7-delta (R=Y and rare-earth elements) compounds, is presented
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