1,721,005 research outputs found
A Coplanar Waveguide Resonator Technique for the Characterization of Iron-Based Superconductors
Full text linkWe present in detail a coplanar waveguide resonator (CPWR) method for the characterization of superconducting single crystals. It exploits the region of a CPWR where the rf magnetic field is quite homogeneous, by coupling a sample to it. Measurements are performed with and without the crystal, allowing a cavity perturbation approach. From the modifications in the resonance frequency and quality factor of the system it is possible to extract the London penetration depth and its anisotropy, quasiparticle conductivity, surface impedance and, when a coexisting magnetic phase is present, even bulk complex susceptibility
s±+d wave multiband Eliashberg theory for the iron pnictides
Full text linkWe calculated the critical temperature in the framework of s± + d-wave
multiband Eliashberg theory. We have solved these equations numerically to see
at what values of the input parameters there is a solution with a non-zero critical
temperature and what is the symmetry of the order parameter of this solution. For
our model we consider the pnictide case with simplifications that allow us to obtain
the most general possible information. For selected and representative cases in which
the order parameter has s± + d symmetry, we calculated the superconducting density
of states, the temperature dependence of the gaps, and the superfluid density so that
comparison with experimental data can be made. Finally, we show that such a system
has only a twofold in-plane symmetry and undergoes a transition from nodal to fully
gapped with increasing temperature
Multiphysics Simulation of a Superconducting Neutron Detector
No full textThe detection of neutrons is crucial for both the operation of nuclear devices and the development of advanced imaging techniques. Recently, a hybrid superconducting niobium-boron sensor on a Si/SiO2 substrate has been developed, aiming for high pulse shape discrimination and controllability of the relaxation time. This device detects thermal neutrons by leveraging the 10B(n,α)7Li reaction in the B layer and the interaction of the charged products with the Nb strip. To critically assess the operation of the Nb-B thermal neutron detector, a multiphysicsmodeling approach is presented here. The software COMSOL Multiphysics is used to provide thermal and electrical responses of this device during the transition-to-normal state and its recovery phase. The study takes into account the impact of the thermal irradiation of the cryostat lid and the joule heating on the operating conditions of the Nb strip. Moreover, a pulsed heat load is introduced in the model to simulate the energy released by either the α or the Li reaction products in the current-biased Nb strip. The SRIM software is used to obtain the deposited power density profiles and theirmean volume of interaction within the sample. For simplicity, the reaction is assumed to take place at the half-thickness of the B layer and the particles propagate perpendicularly to the sample surface. Finally, an iterative procedure was applied to find themost favorable conditions to employ the device in a self-recovering mode by varying both the bias current and the cold finger temperature. This study presents a comprehensive understanding of the working mechanism of the Nb-B thermal neutron detector and proposes a computational approach to find the optimal working point of superconducting neutron detectors
Scaling laws for ion irradiation effects in iron-based superconductors
Full text linkWe report on ion irradiation experiments performed on compounds belonging to the BaFe 2As 2 family, each one involving the partial substitution of an atom of the parent compound (K for Ba, Co for Fe, and P for As), with an optimal composition to maximize the superconducting critical temperature Tc. Employed ion beams were 3.5-MeV protons, 250-MeV Au ions, and 1.2-GeV Pb ions, but additional data from literature are also considered, thus covering a wide range of ions and energies. Microwave characterization based on the use of a coplanar waveguide resonator allowed us to investigate the irradiation-induced Tc degradation, as well as the increase of normal state resistivity and London penetration depth. The damage was quantified in terms of displacements per atom (dpa). From this broad and comprehensive set of experimental data, clear scaling laws emerge, valid in the range of moderate irradiation-induced disorder (dpa up to 5 × 10 - 3 were investigated). In these conditions, linear trends with dpa were found for all the modification rates, while a power law dependence on the ion energy was found for heavy-ion irradiation. All these scaling laws are reported and discussed throughout the paper
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
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