1,721,303 research outputs found
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
Tephra influence on glacier ablation in Iceland
No full textAmong the active volcanoes around the world, approximately one third is covered by perennial snow or ice or is at least located close to glacierized terrain. Explosive eruptions from such volcanoes have the capability to affect extensive glacier areas with fallout of volcanic materials. The resulting supraglacial particle depositions are known to effectively alter the energy balance at the glacier surface. The decreased albedo leads to increased amounts of absorbed energy from the atmosphere, but thermal resistance of the supraglacial deposits hampers the conduction of this energy down to the glacier ice. The counteracting nature of these two effects leads to a high level of complexity and spatial variability in the influences on ablation which are exerted by volcanic fallout. A region of the world where this issue is of particular importance even beyond purely environmental concerns is Iceland. The proximity of major infrastructure installations to active volcanism and wide-spread glaciation and the fact that more than two thirds of all electricity generation on the island comes from predominantly meltwater-fed hydropower plants induces a globally unparalleled socio-economic relevance. This thesis follows an interdisciplinary approach combining methods from geology and physical geography to answer specific research questions that are related to recent eruptions of the Icelandic volcanoes Eyjafjallajökull and Grímsvötn. The influence of volcanic fallout and resulting tephra deposition from these volcanoes on neighboring ice caps is studied with respect to changes in glacier albedo pattern and glacier ablation. Individual links of a modeling chain are presented that reproduce related aspects and processes. Glaciological fieldwork was carried out on Iceland in the period 2013-2016. The data obtained serve as a basis for the development of models of ablation variability under the influence of covers of volcanic materials. New remote sensing-based approaches are developed that quantify changes of glacier albedo across the fallout area. Geological laboratory analyses on samples of volcanic materials from all over Iceland were carried out. The results form the basis for the development of models that estimate the thermal conductivity of a volcanic deposit from rock property data. With the methods and modeling approaches developed it is possible to obtain a spatially distributed quantification of the increases of glacier ablation that may occur under a thin, millimeter-scale deposit of volcanic materials in response to altered albedo. Moreover, it is possible to obtain an estimation of the range of thermal resistivity of a thick, decimeter-scale deposit from geochemical knowledge of the tephra, and thus a quantification of the decreases of ablation under such a deposit. Combining the two approaches facilitates a full estimation of the range of influences of volcanic fallout on glacier ablation. The results hold the potential to be further developed into a model approach capable of filling current gaps regarding volcanic hazard assessment
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
Stratigraphy and diagenesis of the Zechstein 2 in the Southern Permian Basin, onshore northern Netherlands and NW Germany
No full textThe presented thesis focuses on the Upper Permian Zechstein 2 sequence of the German part of the Lower Saxony Basin and onshore the northern Netherlands. The Dutch study area is further divided into three structural elements: the Groningen High in the east, the Lauwerszee Trough, and the Friesland Platform in the west. Both study areas belong structurally to the North German Basin, which is in turn part of the Southern Permian Basin. The Zechstein is characterised by several successive carbonate-evaporite cycles, of which up to seven can be identified in the studied areas today. The second cycle, named the Zechstein 2 (Ca2), is comprised of a carbonate unit at the base, which is overlain by anhydrite and rock salt deposits. The rock salt layer reaches a thickness of more than 500 m in the studied areas and is therefore acting as seal for hydrocarbons trapped in Zechstein rocks, also prohibiting a downward migration of e.g. meteoric fluids into the studied intervals. At least two intra-salt layers, composed of varying amounts of polyhalite and anhydrite, are completely embedded in the Dutch salt unit, but are too thin to be resolved on seismic images. With the help of geophysical well log data, these sub-seismic scale sulphate layers can be correlated and used as stratigraphic markers in the Dutch study area. In order to analyse the precipitation patterns and the diagenetic evolution of the Zechstein 2 sequences, rock samples of overall eight wells were analysed. Petrography methods such as transmitted light microscopy and cathodoluminescence were combined with a large set of analytical techniques, including XRD and XRF analysis, ion chromatography, stable isotope analysis, as well as fluid inclusion analysis. Bromine analysis confirmed that the intra-salt sulphate layers represent freshening events inside the salt basin. Furthermore, geochemical analyses revealed that the underlying Zechstein 2 carbonates in the Lower Saxony Basin were highly affected by late-diagenetic, partially iron-rich, hydrothermal fluids, from which hydrocarbon gases and CO2 were released and trapped in primary and secondary fluid inclusions. The inorganic CO2, derived from the thermal decomposition of underlying Devonian carbonates, is considered as one trigger for carbonate dissolution during burial. However, CO2 alone has no great impact on dissolution, but in combination with late dolomitization and pyrite formation, secondary porosity is created. Thermochemical sulphate reduction (TSR) is a common process in deeply buried sulphate-bearing carbonates and occurred to a great extent in one of the studied wells. In addition to the inorganic CO2 derived from ascending fluids, TSR is considered as an additional source for CO2 in the Lower Saxony Basin. Overall, this study gives new insights into the combined effects of salt tectonics, carbonate diagenesis, burial porosity evolution, and the migration of CO2 derived from inorganic sources
Reservoir quality in the A2C-stringer interval of the late neoproterozoic Ara-Group of the South Oman Salt Basin : diagenetic relationships in space and time
No full textThe carbonate stringers of the Ediacaran-Early Cambrian Ara Group in the South Oman Salt Basin (SOSB) represent a unique intra-salt petroleum system, which has been successfully explored in recent years. However, some of the stringers failed to produce at significant rates due to their complex diagenetic history. Objective of this thesis was therefore to obtain a better understanding of the spatial and temporal distribution patterns of diagenesis and its effect on the reservoir properties within selected carbonate stringers from the late Neoproterozoic A2C interval. Mineralogy, rock fabrics, paragenetic relationships and geochemistry of ~ 400 samples from several petroleum wells were analysed and combined with pre-existing data provided by Petroleum Development Oman (PDO). An integration of the paragenetic sequence derived from thin-section analysis with results from finite element and discrete element models further helps to constrain the effect of salt tectonics on fracture formation and fluid evolution within the stringers. The results of this study comprise crucial information for better prediction of reservoir quality in the analyzed fields, planning of new exploration wells and better volumetric calculations. The integration of thin section analyses with methods such as cathodoluminescence microscopy, isotope and XRD analyses provided a solid basis for the understanding of diagenetic processes in the A2C stringer interval of the SOSB and their implications for the reservoir properties of the stringer play. The observed relationships suggest a close link between carbonate facies and diagenetic products. Together with structural controls these define reservoir quality in the Ara stringer play and it underlines the importance of such an integrated approach for future exploration and production strategies. Petrographic relationships indicate that the grade of cementation from the near-surface and intermediate to the deep burial realm has a large impact on reservoir properties within the studied stringer interval. Anhydrite, reservoir bitumen and dolomite are the most abundant pore filling cement phases. Minor phases include calcite and quartz. Predictable distribution trends are difficult to identify for most of the diagenetic phases. However, some statistically meaningful trends of porosity/permeability and diagenetic phases were observed. Another key result is that dolomite crystal size and sorting of the precursor limestones are further important parameters controlling the porosity/permeability relationship within the study area. Dolomites with large crystal sizes (> 30 μm) typically show the highest permeability for a given interparticle porosity. Dolomite crystal-size distributions could be shown to be facies dependent. Calcite-dominated intervals are often characterised by an almost complete loss of interparticle porosity and permeability. Previously the calcite-dominated intervals were interpreted to be limestones that were not replaced during reflux dolomitisation due to the wedging out of the dolomitising flow and/or their low permeability. However, by a combination of cathodoluminesence and geochemical analyses it could be demonstrated in this study that replacement of dolomite by calcite took place in the intermediate and deep burial realm (especially in Field E). Anhydrite and dolomite dissolved through pressure solution along the stylolites most likely provided the necessary ions for the replacement of dolomite by calcite and additional calcite cementation. Different generations of stylolites were observed within the stringer interval. The Finite Element Models (FEM’s) indicate that stylolite growth started already prior or in initial stages of salt tectonics and most likely continued until recent times. A clear inverse relationship between facies-dependent crystal size and stylolite density is indicated where small crystal sizes seem to promote the process of pressure solution. Another key result of this study is that breakouts and drilling induced/enhanced fractures mapped within the stringer might indicate a present-day, non isotropic in-situ stress field which shows a distribution pattern that is consistent with a radial orientation around the central minibasin, even if salt tectonics already ended in early Ordovician times (~ 498 Ma). The vertical distribution of these features as well as the FEM might indicate a present-day most likely non-isotropic in-situ stress field which might be caused by a small-scale gravitational sinking of the stringers with a total vertical displacement of up to ~ 100 m (0.2 m/Ma)
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
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
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