1,720,984 research outputs found
Ultrastructure and mineral composition of serpulid tubes (Polychaeta, Annelida)
No full textFigure 3. A–B, Neovermilia falcigera, irregularly oriented platy structure, outer tube layer. A, cross section. B, longitudinal section. C–D, Bathyvermilia langerhansi, homogeneous angular crystal structure, outer tube layer. C, cross section. D, longitudinal section. E–F, Pomatostegus stellatus, homogeneous rounded crystal structure. E, cross section. F, longitudinal section. All samples were polished and treated with 1% acetic acid for 2 min. Abbreviations: exter, exterior.Published as part of Vinn, Olev, Ten Hove, Harry A., Mutvei, Harry & Kirsimäe, Kalle, 2008, Ultrastructure and mineral composition of serpulid tubes (Polychaeta, Annelida), pp. 633-650 in Zoological Journal of the Linnean Society 154 (4) on page 639, DOI: 10.1111/j.1096-3642.2008.00421.x, http://zenodo.org/record/544560
Cameral deposits in Paleozoic cephalopods
No full textCalcareous cameral deposits have been described in several orthocerid and actinocerid nautiloids. According to the prevailing hypothesis, they were secreted during the lifetime of the animal, either by living tissues in the shell chambers, or by precipitation from the cameral liquid. In the present paper, cameral deposits are described in three species of Carboniferous orthocerid-like coleoid (Order Colorthocerida) from USA. The shell walls and septa in these coleoids are very thin and poorly calcified. In one half of the population of the three species, the septa are completely fragmented and there are no cameral deposits. In the other half of the population, the septa are partially fractioned and their surfaces are covered by welldeveloped cameral deposits. In contrast to the septa, the cameral deposits do not show any fractioning. To explain the origin of the cameral deposits, the following hypothetical scenario is the most realistic. After the death of the animals, the shells were accumulated on the sea floor and in one half of the population the septa became fully fractioned by the hydrostatic pressure. In shells of another half of the population, the septa were only partially fractioned. The calcifying bacteria entered the chambers of the dead shells through the porous connecting rings and gave rise to the cameral deposits
Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea: siphuncular structure in the Ordovician nautiloid Bathmocerass (Cerphalopoda)
No full textBased on differences in the siphuncular structures, the subclass Nautiloidea is divided into two new superorders: Nautilosiphonata and Calciosiphonata. The first superorder is characterized by the nautilus-type of connecting rings, and the second superorder by calcified-perforate type of the connecting rings. A new order Cyrtocerinida is erected for the families Bathmoceratidae, Cyrtocerinidae and Eothinoceratidae, previously included in the order Ellesmeroceratida. The siphuncular structure in the Ordovician nautiloid Bathmocerasholmi n. sp. is described. It is characterized by (1) connecting rings that are composed of an outer, calcareous, spherulitic–prismatic layer and an inner, fibrous, chitinous layer, and (2) prominent siphuncular ridges that originate from the inner surfaces of the connecting rings. The structure of the siphuncular ridges in Bathmoceras is compared with that of the actinosiphonate lamellae in the Silurian oncocerid nautiloid Octamerella.No funding indicated.</p
Siphuncular structure in the extant Spirula and in other coleoids (Cephalopoda)
No full textThe shell wall in Spirula is composed of prismatic layers, whereas the septa consist of lamello-fibrillar nacre. The septal neck is holochoanitic and consists of two calcareous layers: the outer lamello-fibrillar nacreous layer that continues from the septum, and the inner pillar layer that covers the inner surface of the septal neck. The pillar layer probably is a structurally modified simple prisma layer that covers the inner surface of the septal neck in Nautilus. The pillars have a complicated crystalline structure and contain high amount of chitinous substance. The interspaces between the pillars probably are traversed horizontally by numerous chitinous membranes like in the cuttlebone chambers in Sepia. The connecting ring is composed of similar two layers as that in the extant Nautilus: the outer spherulitic–prismatic layer and the inner chitinous layer. The spherulitic–prismatic layer takes its origin on the outer surface of the septal neck, whereas the inner chitinous layer is the non-calcified continuation of the lamello-fibrillar nacreous layer of the septal neck. The siphuncular structure in Spirula is compared with that in the extant Nautilus, fossil nautilosiphonate nautiloids, and five taxa of coleoids.No funding indicated.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Restudy of some plectronocerid nautiloids (Cephalopoda) from the late Cambrian of China; discussion on nautiloid evolution and origin of the siphuncle
No full textThe sub-class Nautiloidea is divided into two super-orders, Nautilosiphonata and Calciosiphonata, basedon different structural types of the connecting rings.The late Cambrian order Plectronocerida has the calciosiphonate type of connecting ring similar tothat in post-Cambrian orthocerids. It is structurally more complex than the nautilosiphonate connectingring in late Cambrian ellesemerocerid-like nautiloids. The plectronocerid nautiloids, therefore, evolvedfrom the ellesmerocerid-like nautiloids and not vice versa. As indicated by the complex siphuncularstructure in plectronocerids, cephalopod evolution began earlier than previously estimated, probably inthe early Cambrian. The siphuncle in cephalopods originated from a calcareous septum that becamepartially non-calcified and formed the connecting ring
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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