1,721,028 research outputs found
Challenging microwave resonant measurement techniques for conducting material characterization
No full textDielectric loaded resonators, by virtue of their high sensitivity, are a de facto standard for the measurement of the microwave surface impedance Z of good conductors, including superconductors. However, new perspective applications of superconductors request measurements in increasingly extreme conditions: cryogenic and magnetic environments, often combined together. Careful evaluations of the dielectric resonator (DR) design are necessary to operate in these conditions. Moreover, the evaluation of the uncertainties and the issues related to an appropriate calibration become problematic. We present here a performance analysis of DRs designed for cryogenic temperature and high magnetic field operation and some sample experimental results on Z measurements on the most technologically interesting superconductors
Characterisation of dielectric 3D-printing materials at microwave frequencies
Full text link3D-printer materials are becoming increasingly appealing, especially for high frequency applications. As such, the electromagnetic characterisation of these materials is an important step in evaluating their applicability for new technological devices. We present a measurement method for complex permittivity evaluation based on a dielectric loaded resonator (DR). Comparing the quality factor Q of the DR with a disk-shaped sample placed on a DR base, with Q obtained when the sample is substituted with an air gap, allows a reliable determination of the loss tangent
Surface impedance measurements in superconductors in dc magnetic fields: Challenges and relevance to particle physics experiments
No full textParticle physics and radio-frequency (RF) superconductivity have driven each other on since the 1970s. The unique properties of superconductors (SC) have been the enabling keys for the realization of accelerators with always increased performances thanks to the realization of all-superconducting cavities. The use of increasingly pure superconducting coatings for accelerating cavities, with lower and lower RF losses, determined such high-quality factors [1] that the need to operate at low temperatures (below the superconducting transition temperature ) was well paid for. Recently, with respect to the path followed by the high frequency superconductivity [2], a new field opened since SCs are being considered for GHz operation in high dc magnetic fields, and measurements (and optimization) of totally different quantities are needed. The possibility of successfully using SCs in high magnetic fields for these purposes is far from obvious and it depends on the outcome of accurate measurements of usually overlooked quantities
Multi-group analysis of Minor Actinides transmutation in a Fusion Hybrid Reactor
Full text linkNew nuclear technologies are currently being study to face High Level Waste treatment and disposal issues. Generally, GEN-IV fission Fast Reactors (FR) are considered the waste-burners of the future. In fact, a fast flux turns out to be the best choice for actinides irradiation in critical reactors because of favorable cross section conditions. Differently, Fusion Fission Hybrid Reactors (FFHR) are futuristic devices based on the combination of fusion and fission systems and could represent an alternative to FRs. In such systems, the choice spectrum of the neutron flux that irradiates HLW may be non-obvious due to some operational constraints which have to be considered. To design and optimize these systems as waste-burners, one should fully understand the transmutation dynamics occurring into the fission region. A multi-energy-group analysis by FISPACT-II code has been set to analyze the conversion processes in scenarios characterized by different neutron energy spectra and fluences. The results of this study show that, despite fast fluxes are characterized by better behaviors in terms of radiotoxicity treatment, the difficulties of reaching high reaction yields may require solutions involving moderators or broadened neutron fluxes to increase the reactions probabilities and, consequently, actinides mass conversion yield
Physics of vortex motion by means of microwave surface impedance measurements (Review article)
No full textIn this paper we present a short overview on the results that can be obtained through the study of vortex motion at high frequencies. The phenomenological force balance for isolated-like vortices shaken by microwave currents and subjected to viscous drag, pinning forces and thermal creep is recalled and physically presented. The derived vortex motion resistivity, together with the main vortex parameters (viscosity η and flux flow resistivity p ff, pinning constant kp, creep factor χ), is then commented. Sample measurements are reported to illustrate the main aspects of the involved physical models
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
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