1,721,048 research outputs found
High-resolution VLA observations of FR0 radio galaxies: the properties and nature of compact radio sources
Full text linkWe present the results of Karl G. Jansky Very Large Array (VLA) observations regarding the properties of FR0 radio galaxies, the compact radio sources associated with early-type galaxies that represent the bulk of the local radio-loud population of active galactic nuclei. We obtained A-array observations at 1.5, 4.5 and 7.5 GHz for 18 FR0s from the FR0CAT sample: these are sources at z < 0.05, which are unresolved in the FIRST images and spectroscopically classified as low-excitation galaxies (LEGs). Although we reach an angular resolution of ∼0.3 arcsec, the majority of the 18 FR0s are still unresolved. Only four objects show extended emission. Six have steep radio spectra, 11 have flat cores, while one shows an inverted spectrum. We find that (i) the ratio between the core and total emission in FR0s is ∼30 times higher than that in FRIs, and (ii) FR0s have the same properties as FRIs from the nuclear and host points of view. FR0s differ from FRIs only in the paucity of extended radio emission. Various evolutionary scenarios were investigated: (i) the possibility that all FR0s are young sources eventually evolving into extended sources was ruled out by the distribution of radio sizes; (ii) similarly, a time-dependent scenario, in which a variation of accretion or jet launching prevents the formation of large-scale radio structures, appears to be implausible owing to the large abundance of subkiloparsec objects; (iii) a scenario in which FR0s are produced by mildly relativistic jets is consistent with the data but requires observations of a larger sample if it is to be properly tested
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
What drives the radio slopes in radio-quiet quasars?
No full textThe origin of the radio emission in radio-quiet (RQ) quasars is not established yet. Important hints can be provided by the spectral slope, and its relation to other emission properties. We compiled the highest resolution 5 and 8.4 GHz Very Large Array observations available of the RQ optically selected Palomar–Green (PG) quasars at z < 0.5. We derive the 5–8.4 GHz spectral slope, αR, for 25 of the complete and well-studied sample of 71 RQ PG quasars. We find a highly significant correlation of αR with L/LEdd, where high L/LEdd(>0.3) quasars have a steep slope (αR < −0.5), indicative of an optically thin synchrotron source. In contrast, lower L/LEdd(<0.3) quasars generally have a flat slope (αR > −0.5), indicative of a compact optically thick synchrotron source. Flat αR quasars also have a low Fe II/Hβ line ratio, and a flat soft X-ray slope. The 16 radio loud (RL) PGs do not follow the RQ quasar set of correlations, and their αR is set by MBH, suggesting that the radio emission mechanisms in RL and RQ quasars are different. A possible interpretation is that high L/LEdd RQ quasars produce a strong outflow and an associated optically thin synchrotron emission. In lower L/LEdd RQ quasars, the strong outflow is missing, and only a compact optically thick radio source remains, possibly associated with the accretion disc coronal emission. A systematic study of RQ quasars at higher frequencies, and higher resolution, can test whether a compact flat source indeed resides in the cores of all RQ quasars, and allows the exploration of its relation with the coronal X-ray emission.</p
Offerta di Servizi Sociosanitari attraverso la Televisione Digitale Terrestre
No full textQuando nel 2012 la Televisione Analogica terminerà le trasmissioni ed i Decoders del Digitale Terrestre
(DT) saranno nelle case di tutti gli Italiani, gli Enti Pubblici non saranno più giustificati nel fornire
informazioni e servizi solo su Internet. Anche le Aziende Sanitarie dovranno contribuire a ridurre questo
“digital divide” portando sul DT le più importanti informazioni e cogenti servizi erogati attualmente tramite
Internet. La “Multimedia Home Platform” del DT ha però caratteristiche protocollari e strutturali diverse,
per cui è importante capire fin da ora come potranno essere trasportati contenuti dall'ambiente PC allo
scenario televisivo, in cui la capacità d'interazione è ridotta dai limiti imposti dal telecomando. La presenza
del “canale di ritorno” consentirà al cittadino di inviare richieste di servizi all'Azienda e ricevere risposte
personali, garantendo quindi la specificità interattiva e la riservatezz
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
Pilot study of the radio-emitting AGN population: The emerging new class of FR 0 radio-galaxies
Full text linkWe present the results of a pilot JVLA project aimed at studying the bulk of the radio-emitting AGN population, that was unveiled by the NVSS/FIRST and SDSS surveys. The key questions are related to the origin of their radio-emission and to its connection with the properties of their hosts. We obtained A-array observations at the JVLA at 1.4, 4.5, and 7.5 GHz for 12 sources, a small but representative subsample. The radio maps reveal compact unresolved or only slightly resolved radio structures on a scale of 1-3 kpc, with the one exception of a hybrid FR I/FR II source extended over ∼40 kpc. Thanks to either the new high-resolution maps or to the radio spectra, we isolated the radio core component in most of them. We split the sample into two groups. Four sources have low black hole (BH) masses (mostly ∼107 Mo) and are hosted by blue galaxies, often showing evidence of a contamination from star formation to their radio emission, and are associated with radio-quiet (RQ) AGN. The second group consists in seven radio-loud (RL) AGN, which are located in red massive (∼1011 Mo) early-type galaxies, have high BH masses (108 Mo), and are spectroscopically classified as low excitation galaxies (LEG). These are all characteristics typical of FR I radio galaxies. They also lie on the correlation between radio core power and [O III] line luminosity defined by FR Is. However, they are more core-dominated (by a factor of ∼30) than FR Is and show a deficit of extended radio emission. We dub these sources "FR 0" to emphasize their lack of prominent extended radio emission, which is their single distinguishing feature with respect to FR Is. The differences in radio properties between FR 0s and FR Is might be ascribed to an evolutionary effect, with the FR 0 sources undergoing rapid intermittency that prevents the growth of large-scale structures. However, this contrasts with the scenario in which low-luminosity radio-galaxies are fed by continuous accretion of gas from their hot coronae. In our preferred scenario the lack of extended radio emission in FR 0s is due to their lower jet Lorentz Γ factor with respect to FR Is. The slower jets in FR 0s are more subject to instabilities and entrainment, which causes their premature disruption
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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