1,721,389 research outputs found
Full Wave VLF Modes in a Cylindrically Symmetric Enhancement of Plasma Density. Planetary and Space Science
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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
Adaptive optics with an infrared Pyramid wavefront sensor
Full text linkWavefront sensing in the infrared is highly desirable for the study of M-type stars and cool red objects, as they are sufficiently bright in the infrared to be used as the adaptive optics guide star. This aids in high contrast imaging, particularly for low mass stars where the star-to-planet brightness ratio is reduced. Here we discuss the combination of infrared detector technology with the highly sensitive Pyramid wavefront sensor (WFS) for a new generation of systems. Such sensors can extend the capabilities of current telescopes and meet the requirements for future instruments, such as those proposed for the giant segmented mirror telescopes. Here we introduce the infrared Pyramid WFS and discuss the advantages and challenges of this sensor. We present a new infrared Pyramid WFS for Keck, a key sub-system of the Keck Planet Imager and Characterizer (KPIC). The design, integration and testing is reported on, with a focus on the characterization of the SAPHIRA detector used to provide the H-band wavefront sensing. Initial results demonstrate a required effective read noise <1e^– at high gain
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
Approximate nonnegative matrix factorization algorithm for the analysis of angular differential imaging data
Full text linkThe angular differential imaging (ADI) is used to improve contrast in high resolution astronomical imaging. An example is the direct imaging of exoplanet in camera fed by Extreme Adaptive Optics. The subtraction of the main dazzling object to observe the faint companion was improved using Principal Component Analysis (PCA). It factorizes the positive astronomical frames into positive and negative components. On the contrary, the Nonnegative Matrix Factorization (NMF) uses only positive components, mimicking the actual composition of the long exposure images
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
Near-infrared wavefront sensing
Full text linkWe discuss the advantages of wavefront sensing at near-infrared (IR) wavelengths with low-noise detector technologies that have recently become available. In this paper, we consider low order sensing with laser guide star (LGS) adaptive optics (AO) and high order sensing with natural guide star (NGS) AO. We then turn to the application of near-IR sensing with the W. M. Keck Observatory (WMKO) AO systems for science and as a demonstrator for similar systems on extremely large telescopes (ELTs). These demonstrations are based upon an LGS AO near-IR tip-tilt-focus sensor and our collaboration to implement a near-IR pyramid wavefront sensor (PWFS) for a NGS AO L-band coronagraphic imaging survey to identify exoplanet candidates
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