1,720,985 research outputs found
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
Detection of strong activity in the eclipsing binary brown dwarf 2MASS J05352184-0546085: a possible explanation for the temperature reversal
No full textWe show high-resolution spectra of the eclipsing brown dwarf binary 2MASS J05352184 - 0546085 taken at the two opposite radial velocity maxima. Comparisons of the TiO bands to model and template spectra are fully consistent with the temperatures previously derived for this system. In particular, the reversal of temperatures with mass - in which the higher mass primary is cooler than its companion - is confirmed. We measure the projected rotation velocities of the components; the primary is rotating at least twice as rapidly as the secondary. At the two radial velocity maxima, H alpha emission lines of both components stick out to either sides of the H alpha central wavelength, which is dominated by nebula emission. This enables us to model the individual H alpha lines of the primary and the secondary. We find that the H alpha emission from the primary is at least 7 times stronger than the emission from the secondary. We conclude that the temperature reversal is very likely due to strong magnetic fields inhibiting convection on the primary
Detection of White Dwarf companions to Blue Stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
No full textSeveral possible formation pathways for blue straggler stars have been
developed recently, but no one pathway has yet been observationally
confirmed for a specific blue straggler. Here we report the first
findings from a Hubble Space Telescope Advanced Camera for Surveys/Solar
Blind Channel far-UV photometric program to search for white dwarf
companions to blue straggler stars. We find three hot and young white
dwarf companions to blue straggler stars in the 7 Gyr open cluster NGC
188, indicating that mass transfer in these systems ended less than 300
Myr ago. These companions are direct and secure observational evidence
that these blue straggler stars were formed through mass transfer in
binary stars. Their existence in a well-studied cluster environment
allows for observational constraints of both the current binary system
and the progenitor binary system, mapping the entire mass transfer
history
The mass-transfer formation frequency of blue straggler stars in the old open cluster NGC 188
No full textThe formation of blue straggler stars (BSSs), commonly categorized as
stars bluer and brighter than the main sequence turnoff, has puzzled
astronomers since their first detection over sixty years ago. The
well-studied BSS population of the old (7 Gyr) open cluster NGC 188 has
the potential to settle outstanding issues surrounding the frequency of
different BSS formation mechanisms. NGC 188 contains 21 BSSs: 15
long-period single-lined binaries, two short-period double-lined
binaries, and four non-velocity variables. We present results of the
Hubble Space Telescope far-ultraviolet (FUV) ACS/SBC survey of the NGC
188 BSS population. This survey aims to detect white dwarf (WD)
companions of BSSs that are indicative of a mass-transfer formation
history. We directly detect FUV excesses consistent with four hot WD
companions (Teff ≥ 12,000 K). We infer the presence of
three additional WD companions with temperatures between 11,000-12,000
K. Since WDs cool as they age, these results indicate that seven BSSs
formed through mass transfer within the past 400 Myr. These WD
detections set a lower limit mass-transfer formation frequency of 33%.
After taking into account other potential formation mechanisms we
conclude that 14 long-period binary BSSs likely formed through mass
transfer, setting a total NGC 188 BSS mass-transfer formation frequency
of 67%. Comparing these results to a sophisticated N-body model of NGC
188 implies that binary population synthesis models underproduce mass
transfer products, and the parameterization of stable mass transfer may
need to be revisited. Finally, when comparing the optical CMD position
of young BSSs to the zero-age main sequence (ZAMS), we find that
distance from the ZAMS is not necessarily equivalent to BSS age. One
must use caution before using standard single-star isochrones to age
luminous BSSs.Support for Program number 12492 was provided by NASA
through a grant from the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy,
Incorporated, under NASA contract NAS5-26555. This work was funded by
the National Science Foundation grant AST-0908082 to the University of
Wisconsin-Madison
Implications for the formation of blue straggler stars from HST ultraviolet observations of NGC 188
No full textWe present results of a Hubble Space Telescope (HST) far-ultraviolet (FUV) survey searching for white dwarf (WD) companions to blue straggler stars (BSSs) in open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined binaries with properties suggestive of mass-transfer formation via Roche lobe overflow, specifically through an asymptotic giant branch star transferring mass to a main sequence secondary, yielding a BSS binary with a WD companion. In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a WD companion that is hot and luminous enough to be directly detected as a FUV photometric excess with HST. Comparing expected BSS FUV emission to observed photometry reveals four BSSs with WD companions above 12,000 K (younger than 250 Myr) and three WD companions with temperatures between 11,000 and 12,000 K. These BSS+WD binaries all formed through recent mass transfer. The location of the young BSSs in an optical color–magnitude diagram (CMD) indicates that distance from the zero-age main sequence does not necessarily correlate with BSS age. There is no clear CMD separation between mass transfer-formed BSSs and those likely formed through other mechanisms, such as collisions. The seven detected WD companions place a lower limit on the mass-transfer formation frequency of 33%. We consider other possible formation mechanisms by comparing properties of the BSS population to theoretical predictions. We conclude that 14 BSS binaries likely formed from mass transfer, resulting in an inferred mass-transfer formation frequency of approximately 67%
Experimental investigation of the nebular formation of chondrule rims and the formation of chondrite parent bodies
No full textWe developed an experimental setup to test the hypothesis that accretionary rims around chondrules formed in the solar nebula by accretion of dust on the surfaces of hot chondrules. Our experimental method allows us to form dust rims around chondrule analogs while levitated in an inert-gas flow. We used micrometer-sized powdered San Carlos olivine to accrete individual dust particles onto the chondrule analogs at room temperature (20 degrees C) and at 1100 degrees C. The resulting dust rims were analyzed by means of two different techniques: non-destructivemicro computer tomography, and scanning electron microscopy. Both methods give very similar results for the dust rimstructure and a mean dust rim porosity of 60% for the hot coated samples, demonstrating that both methods are equally well suited for sample analysis. The chondrule analog's bulk composition has no measurable impact on the accretion efficiency of the dust. We measured the chemical composition of chondrule analog and dust rim to check whether elemental exchange between the two components occurred. Such a reaction zone was not found; thus, we can experimentally confirm the sharp border between chondrules and dust rims described in the literature. We adopted a simple model to derive the degree of post-accretionary compaction for different carbonaceous chondrites. Moreover, we measured the rim porosity of a fragment of Murchison meteorite, analyzed it with micro-CT and found rim porosities with this technique that are comparable to those described in the literature. (C) 2012 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG) [Bl 298/13-1, SPP 1385
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