1,721,077 research outputs found
Mass Beyond the Main Sequence
No full textBrown dwarfs are now being discovered in significant numbers which means that at last it is possible to be quantitative about their number density and thus their contribution to the stellar neighbourhood. Overall the emerging picture is one of rising mass function into the brown dwarf regime though with a total brown dwarf mass contribution of around 10 percent that due to stars. Contrary to expectation, these stars too small to burn nuclear fuel, do not contribute significantly to our Galaxy's missing mass. However, their properties are more complex than expected and thus there are considerable uncertainties to overcome before a robust determination of the brown dwarf mass function is possible
The UKDMC dark matter xenon programme: New WIMP limits and progress towards 1-tonne
No full textWe outline recent progress from the liquid xenon WIMP search programme at Boulby. This comprises a staged series of three experiments, ZEPLIN I, II and III, aimed simultaneously to improve sensitivity towards 10−8 pb spin independent cross-section and to provide a test-bed for the design of a full-scale 1 tonne detector capable of reaching below 10−9 pb. First preliminary results from ZEPLIN I are presented, yielding a limit approaching 4 × 10−6 pb, with final sensitivity now projected to reach below 10−6 pb with 8 months more running. We describe progress also on the development and construction of ZEPLIN II and III, both of which use simultaneous collection of primary and secondary elecroluminescence signals, plus preliminary design work on the ZEPLIN-MAX 1 tonne experiment
Scattering of Ultrahigh Energy (UHE) Extragalactic Neutrinos onto Light Relic Neutrinos in Galactic HDM Halo Overcoming the GZK Cut off
No full textThe rarest cosmic rays above the GZK cut'off are probably born at cosmic distances ( tens Mpc) by AGNs (QSRs, BLac, Blazars...). Their puzzling survival over BBR radio waves opacities (the ``GZK cut off'') might find a natural explanation if the traveling primordial cosmic rays were UHE neutrinos (born by UHE photopion decay) which are transparent to or BBR. These UHE might scatter onto those (light and cosmological) relic neutrinos clustered around our galactic halo.
The branched chain reactions from a primordial nucleon (via photoproduction of pions and decay to UHE neutrinos) toward the consequent beam dump scattering on galactic relic neutrinos is at least three order of magnitude more efficient than any known neutrino interactions with Earth atmosphere or direct nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV event) might be originated at far distances (as Seyfert galaxy MCG 8-11-11). The needed UHE radiation power is in rough agreement with the NCG 8-11-11 observed in MeV gamma energy total output power. The final chain products observed on Earth by the Fly's Eye detector might be mainly neutron and antineutrons as well as, at later stages, protons and antiprotons. These hadronic products are most probably secondaries of or pair productions and might be consistent with the last AGASA discoveries of 6 doublet and one triplet event
Slowing Down and speeding up PSR's Periods: A Shapiro Telescope tracing Dark Matter
No full textAbstract
Dark matter influence globally galactic Keplerian motions and individually, by microlensing, star's acromatic luminosities. Moreover gravity slows down time as probed by gravitational redshift. Therefore pulsar's (PSR's) periods may record, by slowing and speeding up, any Dark MACHO crossing along the line-of-sight. This phase delay, a Shapiro Phase Delay, is a gravitational integral one and has been probed since 1964 on planets by radar echoes. We discovered in PSRs catalog a few rare PSRs (with negative period derivatives) consistent with speeding up by Shapiro delay due to MACHOs. We propose to rediscover the Shapiro effect on our solar system (for Jupiter, Mars, Sun) to calibrate a new "Shapiro Telescope Array" made by collective monitoring of the sample of PSRs along the ecliptic plane
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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