124,901 research outputs found
Single-Phase 60-K Bulk Superconductor in Annealed Ba2YCu3O7-DELTA(0.3-Less-Than-Delta-Less-Than-0.4) with Correlated Oxygen Vacancies in the Cu-O Chains
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Influence of Mg deficiency on crystal structure and superconducting properties in MgB2 single crystals
No full textThe effects of high-temperature vacuum-annealing-induced Mg deficiency in MgB(2) single crystals grown under high pressure were investigated. As the annealing temperature was increased from 800 to 975 degrees C, the average Mg content in the MgB(2) crystals systematically decreased while T(c) remains essentially unchanged and the superconducting transition slightly broadens from similar to 0.55 to similar to 1.3 K. The reduction in the superconducting volume fraction was noticeable already after annealing at 875 degrees C. Samples annealed at 975 degrees C are partially decomposed and the Mg site occupancy is decreased to 0.92 from 0.98 in as-grown crystals. Annealing at 1000 C completely destroys superconductivity. X-ray diffraction analysis revealed that the main final product of decomposition is polycrystalline MgB(4) and thus the decomposition reaction of MgB(2) can be described as 2MgB(2)(s) --> MgB(4)(s) + Mg(g). First-principles calculations of the Mg(1-x)(V(Mg))(x)B(2) electronic structure, within the supercell approach, show a small downshift of the Fermi level. Holes induced by the vacancies go to both sigma and pi bands. These small modifications are not expected to influence T(c), in agreement with observations. The significant reduction in the superconducting volume fraction without noticeable T(c) reduction indicates the coexistence, within the same crystal, of superconductive and nonsuperconductive electronic phases, associated with regions poor and rich in Mg vacancies
MgB2 single crystals substituted with Li and with Li-C: Structural and superconducting properties
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Effective mass measurement: influence of hole band non parabolicity in SiGe/Ge quantum wells
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