1,721,338 research outputs found
An H2Co 6 cm maser pinpointing a possible circumstellar torus in IRAS 18566+0408
Get PDFArtículo de publicación ISIWe report observations of 6 cm, 3.6 cm, 1.3 cm, and 7 mm radio continuum, conducted with the Very Large Array, toward IRAS 18566+0408, one of the few sources known to harbor H(2)CO6 cm maser emission. Our observations reveal that the emission is dominated by an ionized jet at centimeter wavelengths. Spitzer IRAC images from GLIMPSE support this interpretation, given the presence of 4.5 mu m excess emission at approximately the same orientation as the centimeter continuum. The 7 mm emission is dominated by thermal dust from a flattened structure almost perpendicular to the ionized jet; thus, the 7 mm emission appears to trace a torus associated with a young massive stellar object. The H2CO 6 cm maser is coincident with the center of the torus-like structure. Our observations rule out radiative pumping via radio continuum as the excitation mechanism for the H2CO 6 cm maser in IRAS 18566+0408
SMA Observations of the Hot Molecular Core IRAS 18566+0408
Get PDFWe present Submillimeter Array (SMA) observations toward the high-mass star-forming region IRAS 18566+0408. Observations at the 1.3 mm continuum and in several molecular line transitions were performed in the compact (2ʺ4 angular resolution) and very-extended (~0ʺ4 angular resolution) configurations. The continuum emission from the compact configuration shows a dust core of 150 M ⊙, while the very-extended configuration reveals a dense (2.6 × 107 cm−3) and compact (~4000 au) condensation of 8 M ⊙. We detect 31 molecular transitions from 14 species including CO isotopologues, SO, CH3OH, OCS, and CH3CN. Using the different k-ladders of the CH3CN line, we derive a rotational temperature at the location of the continuum peak of 240 K. The 12CO(2–1), 13CO(2–1), and SO(65–54) lines reveal a molecular outflow at PA ~ 135° centered at the continuum peak. The extended 12CO(2–1) emission has been recovered with the IRAM 30 m telescope observations. Using the combined data set, we derive an outflow mass of 16.8 M ⊙. The chemically rich spectrum and the high rotational temperature confirm that IRAS 18566+0408 is harboring a hot molecular core. We find no clear velocity gradient that could suggest the presence of a rotational disk-like structure, even at the high-resolution observations obtained with the very-extended configuration
Discovery of an H2CO 6 centimeter maser in IRAS 18566+0408
No full textWe report VLA observations toward IRAS 18566+0408 conducted to determine the nature of the H2CO 6 cm emission line recently detected by Araya and coworkers. Our observations clearly show that the H2CO source is due to maser emission, making IRAS 18566+0408 only the fourth Galactic H2CO 6 cm maser source, out of five known H2CO emitters. We also report detection of a weak 2 cm continuum source that is coincident with the H2CO maser. Given the current observational constraints, the maser could be due to the radiative pumping mechanism proposed by Boland & de Jong; however, the coincidence of the new H2CO maser with 22 GHz H2O masers suggests that shocked molecular gas could also play a role in its excitation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Quasi-periodic formaldehyde maser flares in themassive protostellar object IRAS 18566+0408
No full textWe report results of an extensive observational campaign of the 6 cm formaldehyde maser in the young massive stellar object IRAS 18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using the Arecibo Telescope, the Very Large Array, and the Green Bank Telescope, we discovered quasi-periodic formaldehyde flares (P ~ 237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H2CO) and methanol (CH3OH) masers. The H2CO and CH3OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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