1,720,974 research outputs found
FPGA-based, Pound-Drever-Hall electronics and automatic relock
No full textA key component of a compact, portable, robust and turn-key optical local oscillator constituted by a laser whose frequency is referenced to that of one of the longitudinal modes of an optical cavity is the automatic relocking of the laser to the same cavity mode, which is essential for unattended, reliable use in an industrial environment.
In the framework of an EU-funded Joint Reasearch Project, we have adopted a solution based on a field programmable gate array (FPGA). The error signal is generated by means of the Pound-Drever-Hall (PDH) method, using digital signal processing (DSP) in the FPGA. The FPGA also allows the whole system to be controlled (changing the locking parameters is very easy) and integrates an automatic, fast relock algorithm to the same cavity mode.
Because all the signals are available in a digitized form and fast DSP is available in the FPGA, other functions can be implemented, e.g. to characterize and optimize the laser locking system.
In the FPGA board, the PI filter and the automatic lock/relock feature have been tested in a real system available at INRIM. Typical relock time was found to be less then 20 ms for a cavity with a nominal linewidth of 70 kH
Rayleigh scattering for pressure assessment
Full text linkThis paper reports about the realization of a pioneering system for pressure measurements, currently tested up to 400 kPa, based on the Rayleigh scattering and with no mechanical parts interacting with the gas. The preliminary results showed that the device exhibits a strong linear dependence between gas pressure and scattered light, of the order of 10-5, paving the way for promising innovative realizations of scattering-based system for pressure measurement with a single and simple device in a wide pressure range between 10 Pa and 1 MPa
Redundancy-enabled stabilisation of linear encoder performance: The biSLIDER
Full text linkLinear encoders are widely used in industry particularly for machine tools. Their performance may suffer thermal and mechanical instability. This paper presents a technique to stabilise the performance over time by recovering to a reference state. It is based on the simultaneous readings of two heads separated by an invariant spacer. It requires off-the-shelf components only and is widely applicable in industry. Experimental results in the field and in lab show excellent error recovery even in the presence of highly nonlinear errors
1D measurement of coordinates in space: a novel apparatus
Full text linkA novel instrument to measure the coordinate of a point in space is presented. It does so in isolation, i.e. without the aid of similar devices measuring the other coordinates, as it is usually the case with other coordinate instruments. The eventual goal is to achieve a full 3D measurement by replicating the device three times orthogonal to each other, with a target uncertainty of 50 μm over a volume of (10 x 10 x 5) m3 in harsh conditions
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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