1,720,977 research outputs found
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
Fully automated apparatus for thermal diffusivity measurements on HTSC in high magnetic field
No full textThis paper describes an apparatus to measure the thermal diffusivity of high temperature superconductors in an extended range of temperature (10-300 K) and magnetic field (up to 8 T). Heat losses are taken into account by adopting an ac technique. Effects introduced by power dissipated on the heater and thermal contacts between thermocouples and sample are considered. In fact the presence of a thermocouple relaxation time not negligible in respect to the sample relaxation time causes an error in the thermal diffusivity evaluation (up to 13% in a sample with poor thermal contact). We have estimated that, also at the higher temperatures, frequencies over 0.03 Hz keep the thermal losses low enough; in this case the poor thermal contact of the thermocouples can be a major problem. All of the experiment is computer controlled. The accuracy of the measurement, mainly determined by evaluation of the sample length, is 10%, while the sensitivity to the relative variations is much higher (0.1%)
Synthesis and physical properties of the YNi2B2C superconducting phase
No full textWe report the synthesis procedure and the chemical-physical characterization for the YNi2B2C superconductor. From magnetic measurements we show that this material is a type II superconductor. We value the penetration depth, the coherence length and so the Ginzburg -Landau parameter. Despite the low value of kappa (12), a very large region of reversibility in the H-T plane is detected
Thermoelectric and thermomagnetic effects in the mixed state analysis of the thermal angle
No full textIn this paper thermoelectric and thermomagnetic coefficients in the mixed state are discussed. Besides the contribution of the Abrikosov vortices, also the role of the vortex-antivortex pairs and of the quasi-particles unbounded and localized in the vortex core is considered. The vortex-antivortex contribution to the Seebeck and Nernst effects is calculated in detail. To study the role of normal excitation we propose to measure the thermal angle, alpha(th) that represents the direction of the vortex velocity. In fact, taking the unbounded quasiparticles into account, or not, as the temperature varies, alpha(th) shows an important difference in behavior, easy to detect experimentally. Measurements of the Seebeck effect and Nernst effect on a Bi(2223) tape are presented and the thermal-angle behavior is discussed. The experimental data are in agreement with the models that consider the unbounded quasiparticles contribution, but some caution must be taken as to the role of the Josephson vortices
Supercurrent lengthscale in sintered YBCO and critical state model.
No full textMagnetization measurements on sintered YBa2Cu3O7−y in two geometries (slab and cylinder) show the coexistence of two transport mechanisms: intergranular and intragranular currents. Both mechanisms can be explained in the framework of the critical state model. Using a simple law for the critical current versus magnetic field dependence, it is possible to calculate the magnetization and the in-phase and out-of-phase AC susceptibility and the agreement with the experimental data is good. Magnetization measurements on tubular samples have been performed too; these measurements, together with χAC measurements allow to determine the dimensions of magnetized regions
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
A.C. susceptibility and magnetization of high-Tc superconductors: Critical state model for the intergranular region
No full textA.C. susceptibility and magnetization measurements on a sintered YBa2Cu3O7−y sample are presented.
The measured magnetization is separated into two terms: one depending on the grains, the other on the intergranular region magnetization. For intergranular region we intend a desordered array of holes surrounded by a shell whose thickness is λ at the surface of the grains connected through Josephson junctions. At these holes the fluxoids are pinned.
In presence of a fluxoid gradient, a net macroscopic magnetization current results from the sum of all the microscopic components, as in the traditional type II superconductors.
The contribution of the intergranular region to the magnetization is well explained in terms of the critical state model, if a critical current density strongly dependent on the magnetic field is assumed
Magnetization decay and pinning energy in a BSCCO single crystal: a comparison between different methods of measurement
No full textThe magnetization decay in a BSCCO single crystal was measured by two different methods: in the first way the decay is observed in the time after stopping the magnetic field, in the second one various hysteresis loops are performed at different field sweep rate.
Using this two methods of measurements we investigate both flux creep regime both the thermally assisted flux flow regime and, in the creep regime, we calculated the energy pinning Uo. The two methods give different values: an explanation for this discrepancy is proposed
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