1,720,995 research outputs found
ANALYSIS OF THE EARLY-TIME OPTICAL SPECTRA OF SN 2011fe IN M101
No full textThe nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s[superscript –1]) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s[superscript –1]. This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s[superscript –1]. The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
Rotationally resolved spectroscopy of asteroid pairs: No spectral variation suggests fission is followed by settling of dust
No full textThe fission of an asteroid due to fast rotation can expose sub-surface material that was never previously exposed to any space weathering process. We examine the spectral properties of asteroid pairs that were disrupted in the last 2 million years to examine whether the site of the fission can be revealed. We studied the possibility that the sub-surface material, perhaps on one hemisphere, has spectral characteristics differing from the original weathered surface. This was achieved by performing rotationally-resolved spectroscopic observations to look for local variations as the asteroid rotates. We spectrally observed 11 asteroids in pairs in the near-IR and visible wavelength range. Photometric observations were also conducted to derive the asteroid lightcurves and to determine the rotational phases of the spectral observations. We do not detect any rotational spectral variations within the signal-to-noise of our measurements, which allows us to tightly constrain the extent of any existing surface heterogeneity. For each observed spectrum of a longitudinal segment of our measured asteroids, we estimate the maximal size of an un-detected “spot” with a spectral signature different than the average. For five asteroids the maximal diameter of such a “spot” is smaller by a factor of two than the diameter of the secondary member of the asteroid. Therefore, the site of the fission is larger than any area with a unique spectral parameters. This means the site of the fission does not have a unique spectrum. In the case of an ordinary chondrite asteroid (S-complex), where the site of fission is expected to present non-weathered spectra, a lack of a fission “spot” (detectable spectroscopically) can be explained if the rotational-fission process is followed by the spread of dust that re-accumulates on the primary asteroid and covers it homogeneously. This is demonstrated for the young Asteroid 6070 that presents an Sq-type spectrum while its inner material, that is presumably revealed on the surface of its secondary member, 54827, has a non-weathered, Q-type spectrum. The spread of dust observed in the disintegration event of the Asteroid P/2013 R3, might be an example of such a process and an indication that P/2013 R3 was indeed formed in a rotational-fission event.AXA Research Fund (Postdoctoral Fellowship)Carnegie Institution of WashingtonNational Science Foundation (U.S.) Astronomy and Astrophysics Postdoctoral ProgramUnited States. National Aeronautics and Space Administration. Planetary Astronomy Program (Grant NNX12AL26G)Space Telescope Science Institute (U.S.) (Hubble Fellowship grant HST-HF-51319.01-A
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Observations of “fresh” and weathered surfaces on asteroid pairs and their implications on the rotational-fission mechanism
Full text linkThe rotational-fission of a “rubble-pile” structured asteroid can result in an “asteroid pair” – two unbound asteroids sharing nearly identical heliocentric orbits. Models suggest that this mechanism exposes material from below the progenitor surface that previously had never have been exposed to the weathering conditions of space. Therefore, the surfaces of asteroid pairs offer the opportunity to observe non-weathered “fresh” spectra.
Here we report near-infrared spectroscopic observations of 31 asteroids in pairs. In order to search for spectral indications of fresh surfaces we analyze their spectral slopes, parameters of their 1 μm absorption band and taxonomic classification. Additionally, through backward dynamical integration we estimate the time elapsed since the disintegration of the pairs’ progenitors.
Analyzing the 19 ordinary chondrite-like (S-complex) objects in our sample, we find two Q-type Asteroids (19289 and 54827) that are the first of their kind to be observed in the main-belt of asteroids over the full visible and near-infrared range. This solidly demonstrates that the Q-type taxonomy is not limited to the NEA population.
The pairs in our sample present a range of fresh and weathered surfaces with no clear evidence for a correlation with the ages of the pairs. However, our sample includes “old” pairs (2 × 106 ⩾ age ⩾ 1 × 106 years) that present relatively low, meteoritic-like spectral slopes (<0.2% per μm). This illustrates a timescale of at least ∼2 myr before an object develops high spectral slope that is typical for S-type asteroids.
We discuss three mechanisms that explain the existence of weathered pairs with young dynamical ages and find that the “secondary fission” model (Jacobson, S.-A., Scheeres, D.-J. [2011]. Icarus 214, 161–178) is the most robust with our observations. In this mechanism an additional and subsequent fission of the secondary component contributes the lion share of fresh material that re-settles on the primary’s surface and recoats it with fresh material. If the secondary breaks loose from the vicinity of the primary before its “secondary fission”, this main source of fresh dust is avoided. We prefer this secondary fission model since (i) the secondary members in our sample present “fresh” parameters that tend to be “fresher” than their weathered primaries; (ii) most of the fresh pairs in our sample have low size ratios between the secondary and the primary; (iii) 33% of the primaries in our sample are fresh, similar to the prediction set by the secondary fission model (Jacobson, S.-A., Scheeres, D.-J. [2011]. Icarus 214, 161–178); (iv) known satellites orbit two of the pairs in our sample with low size ratio (D2/D1) and fresh surface; (v) there is no correlation between the weathering state and the primary shape as predicted by other models.National Science Foundation (U.S.) (Astronomy and Astrophysics Postdoctoral fellowship program)United States. National Aeronautics and Space Administration (NASA Near-Earth Object Observation program, Grant NNX10AG27G)National Science Foundation (U.S.) (Grant 0907766)United States. National Aeronautics and Space Administration (NASA Grant NNX12AL26G)Space Telescope Science Institute (U.S.) (Hubble Fellowship Grant HST-HF-51319.01-A)United States. National Aeronautics and Space Administration (Association of Universities for Research in Astronomy, Inc., NASA, Contract NAS 5- 26555)Czech Science Foundation (Grant 209/12/0229)Poland. National Science Centre (Grant Number NCN 2012/04/S/ST9/00022)National Science Foundation (U.S.) (Grant 6920422)University of Hawaii. Institute for Astronomy (Cooperative Agreement NCC 5-538 with NASA, Science Mission Directorate, Planetary Astronomy Program
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