1,721,087 research outputs found
Heavy metals in intermediate He-rich hot subdwarfs: the chemical composition of HZ 44 and HD 127493
No full textContext. Hot subluminous stars can be spectroscopically classified as subdwarf B (sdB) and O (sdO) stars. While the latter are predominantly hydrogen deficient, the former are mostly helium deficient. The atmospheres of most sdOs are almost devoid of hydrogen, whereas a small group of hot subdwarf stars of mixed H/He composition exists, showing extreme metal abundance anomalies. Whether such intermediate helium-rich (iHe) subdwarf stars provide an evolutionary link between the dominant classes is an open question.
Aims. The presence of strong Ge, Sn, and Pb lines in the UV spectrum of HZ 44 suggests a strong enrichment of heavy elements in this iHe-sdO star and calls for a detailed quantitative spectral analysis focusing on trans-iron elements.
Methods. Non-local thermodynamical equilibrium model atmospheres and synthetic spectra calculated with TLUST
MSST observations of the pulsating sdB star PG 1605+072
No full textWe present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (also known as EC 14026 stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in May/June 2002 immediately following the Whole Earth Telescope Xcov22 run, which observed PG 1605+072 as an alternate target. We will first give an overview of the project and its feasibility, after which we will present the massive data set, made up of 399 h of photometry and 151 h of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and lambda-dependence of photometric amplitudes, and to use these properties for mode identification
Energized uptake of sugars from the apoplast of leaves: A study of some plants possessing different minor vein anatomy
No full textSolutions of sucrose, glucose, raffinose, and stachyose were fed via the petiole to detached leaves of plant species known to transfer sugars during photosynthesis into the phloem using either the apoplastic or the symplastic pathway of phloem loading. Symplastic phloem loaders, which translocate raffinose-type oligosaccharides and sucrose in the phloem, and apoplastic plants, translocating exclusively sucrose, were selected for this study. As the sugars arrived with the transpiration stream in the leaf blade within little more than a minute, dark respiration increased. Almost simultaneously, fluorescence of a potential-indicating dye, which had been infiltrated into the leaves, indicated membrane depolarization. Another fluorescent dye used to record the apoplastic pH revealed apoplastic alkalinization that occurred with a slight lag phase after respiration and membrane depolarization responses. Occasionally, alkalinization was preceded by transient apoplastic acidification. Whereas membrane depolarization and apoplastic acidification are interpreted as initial responses of the proton motive force across the plasma membrane to the advent of sugars in the leaf apoplast, the following apoplastic alkalinization showed that sugars were taken up from the apoplast into the symplast in cotransport with protons. This was true not only for glucose and sucrose, but also for raffinose and stachyose. Similar observations were made for sugar uptake not only in leaves of plants known to export sugars by symplastic phloem loading but also of plants using the apoplastic pathway. Increased respiration during sugar uptake revealed tight coupling between respiratory ATP production and ATP consumption by proton-translocating ATPase of the plasma membrane, which exports protons into the apoplast, thereby compensating for the proton loss in the apoplast when protons are transported together with sugars into the symplast. The extent of stimulation of respiration by sugars indicated that sugar uptake was not limited to phloem tissue. Ratios of the extra CO2 released during sugar uptake to the amounts of sugars taken up were variable, but lowest values were lower than 0.2. When a ratio of 0.2 is taken as a basis to calculate rates of sugar uptake from observed maxima of sugar-dependent increases in respiration, rates of sugar uptake approached 350 nmol/(m(2) leaf surface s). Sugar uptake rates were half-saturated at sugar concentrations in the feeding solutions of about 10-25 mM indicating a low in vivo affinity of sugar uptake systems for sugars
Subluminous O stars
No full textWe report results of spectral analyses of sdO stars selected from the Supernova la Progenitor Survey, the Hamburg Quasar Survey and the Sloan Digital Sky Survey and based on state-of-the-art NLTE model atmospheres. By combining the sdO with the sdB samples we discuss trends of the atmospheric parameters in order to search for evidence for possible evolutionary linkage. The He-sdO stars are found to cluster near T-eff = 45 000 K, log g = 5.5, whereas the number of sdO stars in this area is very small. The "cooler" sdO stars seem to form an extension to the sdB sequences. A couple of sdO stars are obviously evolved from the extended horizontal branch and reach temperatures as high as 80000 K. We conjecture that the He-sdO stars and sdO/sdB stars have a different evolutionary origin. This is corroborated by the much lower binary frequency of the former. Strong enrichments of iron group elements are discovered for hydrogen-rich sdO stars as well as for sdB stars from high resolution UV spectra and have severe implications for the temperature scale. We finally highlight the discovery of a hyper-velocity He-sdO star with a radial velocity of 708 km s(-1) unbound to the Galaxy
Subluminous O stars
No full textWe report results of spectral analyses of sdO stars selected from the Supernova la Progenitor Survey, the Hamburg Quasar Survey and the Sloan Digital Sky Survey and based on state-of-the-art NLTE model atmospheres. By combining the sdO with the sdB samples we discuss trends of the atmospheric parameters in order to search for evidence for possible evolutionary linkage. The He-sdO stars are found to cluster near T-eff = 45 000 K, log g = 5.5, whereas the number of sdO stars in this area is very small. The "cooler" sdO stars seem to form an extension to the sdB sequences. A couple of sdO stars are obviously evolved from the extended horizontal branch and reach temperatures as high as 80000 K. We conjecture that the He-sdO stars and sdO/sdB stars have a different evolutionary origin. This is corroborated by the much lower binary frequency of the former. Strong enrichments of iron group elements are discovered for hydrogen-rich sdO stars as well as for sdB stars from high resolution UV spectra and have severe implications for the temperature scale. We finally highlight the discovery of a hyper-velocity He-sdO star with a radial velocity of 708 km s(-1) unbound to the Galaxy
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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