1,721,223 research outputs found
High-frequency measurement of the interferometric phase, the Faraday rotation, and the Cotton-Mouton effect with a single detector in a far-infrared interferometer-polarimeter
No full textA novel polarization modulation method is proposed, for a possible application in the measurement of the electron density and magnetic field profiles by an interferometer-polarimeter diagnostic in the Divertor Test Tokamak (DTT) device. Starting from the output of a CO2 pumped CHCOH3 far-infrared (FIR) laser (lambda = 118.8 mu m), three waves with frequencies omega, omega - delta omega, and omega + delta omega are generated and coherently combined to produce a polarization modulated laser beam suitable to probe the DTT plasma in a multichord, double-pass scheme. A second, coherently pumped, FIR cavity operating at the slightly detuned omega ' frequency, acts as a local oscillator for the interferometric measurement. By this polarization modulation method, it is possible to simultaneously measure the interferometric phase, the Faraday rotation angle, and the Cotton-Mouton effect, all by a single detector, while keeping to an acceptable value the perturbation of the interferometric phase due to the time modulated polarization. In this paper, we describe the principles of the method and discuss its possible application in the poloidal interferometer-polarimeter diagnostic of the DTT device. A single chord mock-up experiment is in preparation to experimentally test the technique
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
Exploring the Hubble tension with a late time Modified Gravity scenario
No full textWe investigate a modified cosmological model aimed at addressing the Hubble tension, considering revised dynamics in the late Universe. The model introduces a parameter c affecting the evolution equations, motivated by a modified Poisson algebra inspired by effective Loop Quantum Cosmology. Our analysis includes diverse background datasets such as Cosmic Chronometers, Pantheon+ Type Ia Supernovae (with and without the SH0ES calibration), SDSS, DESY6 and DESI Baryon Acoustic Oscillations, and background information of the Cosmic Microwave Background. We find that the model alleviates the Hubble tension in most of the dataset combinations, with cases reducing discrepancies to below 1σ when including SH0ES. However, the model exhibits minimal improvement in the overall fit when compared to ΛCDM, and Bayesian evidence generally favors the standard model. Theoretical foundations support this approach as a subtle adjustment to low-redshift dynamics, suggesting potential for further exploration into extensions of ΛCDM. Despite challenges in data fitting, our findings underscore the promise of small-scale modifications in reconciling cosmological tensions
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
Performance analysis and application study of a laser enhancement cavity for photo-neutralization of Negative Ion Beams
No full textPhoto-neutralization of negative ion beams is now regarded as a promising concept to enhance plasma heating system efficiency of negative ion based neutral beam injection in large fusion experiments. In this work we describe a photoneutralization scheme currently under test at Consorzio RFX based on the trapping of the second harmonic of a Nd:YAG laser in a closed loop optical cavity. In this work the system performances are analyzed with respect to optical layout and optical losses, in order to identify an optimal configuration, as well as to validate a simple numerical model. The latter is developed to assess the photo-neutralization degree achievable once the system is applied to the NIO1 negative ion beam facility in Padova. In particular, the study defines the requirements of pumping laser energy and repetition rate. A parallel analysis, regarding the application of a resonating enhancement cavity to NIO1, is presented and a comparison between the two approaches is discussed
Dispersion scanning beam medium infra-red interferometry for divertor plasma density measurement in DTT
No full textDispersion Interferometers (DI) present the fundamental advantage over conventional ones to be insensitive to mechanical vibrations without requiring a second wavelength interferometer to measure path length variations. On the other hand, their optical setup requires duplication of nearly all optical components for any measuring chord. This makes the realization of a multi-channel interferometer that is needed to obtain density profiles via Abel inversion of line integral measurements more complicated. To overcome such drawback of the DI, in this work we propose to join the dispersion technique to the beam scanning one, which has been already successfully implemented in the conventional mid-infrared two-colour interferometer. In particular, we present a preliminary design of a DI scanning interferometer for the new Divertor Test Tokamak (DTT) facility, presently in construction. DTT is designed to study a large suite of alternative divertor magnetic configurations in order to ensure acceptable conditions at the walls while maintaining sufficient core performance. In this contest, measuring plasma parameters in the divertor region is very important though it often presents various difficulties. To improve divertor measurements the proposed interferometer will measure the density along the divertor legs from the strike points up the X-point. The interferometer will use a CO2 laser (λ =10.6 μm) and a double pass optical scheme. Phase modulation method will be used to improve the resolution of the measurement and to extend the measuring range above the 1020 m-2 line integral limitation of the standard homodyne implementation. Both improvements are important in this application, considering the wide density range expected in the DTT divertor region. Comparing to shorter wavelengths, more commonly used in the DI interferometers, the CO2 wavelength improves density resolution while providing good immunity to the diffraction effect due to the expected high density gradient
Design of an interferometer/polarimeter for DTT
No full textLaser interferometer/polarimeter systems are used in magnetically confined fusion experiments for simultaneous measurements of the line-integrated electron density and of the current-induced magnetic field. In this work, we present the design of the interferometer/polarimeter system for the Divertor Tokamak Test facility (DTT), a new tokamak device dedicated to investigate alternative power exhaust solutions for the nuclear fusion DEMOnstration Power Station (DEMO). The optical design is based on the exploitation of a 7+7 chords scheme, which allows determining density and poloidal field, contributes to evaluate the plasma magnetic equilibrium and can provide the real time estimate of the q profile. Since the optical scheme is thought to be compatible with a possible Double Null divertor configuration, an equatorial port is recommended. In order to protect the in-vessel optics, each chord employs a back reflecting mirror installed in the high field side inner wall close to the divertor, where some plasma-free space is available, and one retroreflector installed in the space behind the low field side outer first wall. With respect to polarimetric measurements and low effects of density gradients, the optimal laser source solution would be 100/50 μm. With this setup, in low/medium density conditions, the longer wavelength will provide a good magnetic field measurement, while the shorter wavelength will allow vibration compensation for density measurements. In high-density regimes, the short wavelength alone can provide both magnetic field information from Faraday rotation and density measurements from the Cotton-Mouton effect. The two wavelengths are close enough to each other also to provide a good sharing of optical components
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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