1,721,017 research outputs found
Experimental analysis of the thermal behavior of a GM cryocooler based on linear system theory
Full text linkClosed cycle refrigerators for cryogenic temperatures (cryocoolers) provide a convenient solution in a wide range of applications, from low temperature physics to cryopumping, superconducting magnets or low noise infrared sensing. Understanding in detail the physical mechanisms underlying cryocooler operation is then of practical and fundamental interest. This paper deals with the analysis as a linear dynamical system of a GM cryocooler operation, considered over a limited range of temperature around a setpoint. The method is interesting as a way to model the thermal behavior of the refrigerator that can be effective in systematic analysis of cryocoolers thermal behaviour and design of temperature controllers
Exploiting First and Second Shapiro Steps Towards the Reduction of Bias Lines in Programmable Josephson Arrays
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Characterization of a Josephson array for pulse-driven voltage standard in a cryocooler
Full text linkPulse-driven Josephson junctions allow the synthesis of very precise both spectrally pure and arbitrary wave forms with frequencies up to the megahertz range. We investigated the properties relevant for metrological applications of series arrays with 4000 Josephson junctions fabricated at PTB in cryocooler and liquid helium. DC electrical parameters were evaluated and Shapiro steps dependence on operating conditions was studied. Both cooling techniques provided similar results for all relevant parameters. In particular, we were able to observe Shapiro step widths of more than 1 mA in cryocooler. Yet, we found that some specific effects related to the different thermal conditions must be taken into account for proper operation in cryocooler
Superconductivity in primary voltage metrology at INRiM
No full textPrimary electrical Metrology is among the first and, to date, one of the most active and successful research field for superconducting devices. Voltage standards based on the Josephson effect are in use since few years after it discovery and have enormously reduced the uncertainty of DC voltage calibrations. INRIM the Italian National Metrology Institute has a long tradition in research on the application of superconductivity to electrical standards. This paper is an overview of main results and ongoing activities
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
Towards a He-Free Source of Arbitrary Quantum Voltage Signals
No full textThe Josephson effect is worldwide exploited as the basis for constant reference voltages in National Metrological Institutes (NMIs) and in industry calibration laboratories. Lately, voltage metrology research has been mainly directed towards the application of Josephson effect for the synthesis of very accurate ac and arbitrary voltage signals: pulse-driven Josephson arrays represent the most promising way for linking ac voltage calibrations to a quantum phenomenon. Furthermore, an easy and secure cooling system based on cryocoolers is desirable in order to allow the spread of Josephson standards outside NMIs. A Gifford-McMahon cryocooler is currently in use at INRiM for the operation of ac-Josephson Voltage Standards (JVSs). We employed pulse-driven JVSs for synthesizing sine waves with frequency in the kHz range and amplitudes in the mV range, with distortion around 80 dBc. In this report we present a detailed description of this technique and of the refrigeration system employed
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