1,721,117 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
Dauerhaftigkeits- und Brandeigenschaften von Carbonfaser-Komposit verstärktem Holz
Full text linkThe timber construction industry is considered to have a high potential in relation to the climate crisis. Carbon sequestration, low process energy requirements and lightweight construction are some of the advantages of building with wood but its market share, especially in multi-story buildings, is comparatively low. To increase its competitiveness with reinforced concrete and steel structures, hybrid materials combining carbon fiber-reinforced polymers (CFRP) and wood promise high potential. The addition of just a fraction of high strength and high modulus carbon fibers, can significantly increase the overall strength and stiffness of a wood structural member. As a tensile reinforcement, the ductility of wood structures can be increased. The failure mode of timber beams can be changed from brittle tensile to ductile compression failure. In addition, high safety factors are used to account for the natural variation of wood and wood products. With FRP-reinforcement, this variation could be reduced, making the use of wood more economical and environmentally friendly. However, there is a challenge in the interfacial bonding between the FRP reinforcement and the wood, which directly affects the short- and long-term performance of the composite. Wood, carbon fibers and thermoset polymers have different thermal and hygric expansions, elasticities and strengths, which can lead to delamination under unfavorable environmental conditions. In addition, to maximize gain, and in retrofit applications, where access is also limited, reinforcements are often positioned as the outermost layer of structural members. These locations are not only susceptible to environmental exposure but also to rapid heating in the event of a fire. The thermoset matrix systems are not only flammable, but can also lead to rapid failure of the CFRP reinforcement due to their low glass transition temperatures of 50 to 150°C. In order to support the safe use of CFRP- timber in the construction industry, additional research is needed. This dissertation focuses on the durability of epoxy resin bonded CFRP-wood under various environmental conditions. The short-term, long-term and fire performance of CFRP-wood were investigated. Possible improvements by modifying the surface of the wood prior to bonding such as priming with dimethylformamide, silanization with aminopropyltriethoxy- and octadecyltrichloro- silane as well as delignification with peracetic acid were investigated. Various tests were performed, including quasi-static and dynamic mechanical analysis tests, natural and artificial weathering and long-term stress analysis. Supporting investigations included chemical and microstructural studies of the surface and bond. Durability in high temperature environments, such as fire, was investigated in small-scale to bench-scale fire performance analysis. The fire performance of the thermoset matrix, carbon fiber reinforced polymer and CFRP-wood was analyzed and optimized using a statistical design- of-experiments (DoE) approach. Further statistical analyses were performed on all results to determine the significance of the effects found. The main contents of this dissertation are structured in three parts. (1) Chapter 4 contains the quantitative quasi-static and dynamic analysis of the shear, tensile and flexural properties of the thermoset matrix, wood and CFRP-wood on different scales. Also, supporting mechanical, chemical analyses were carried out to determine effects of chemical modifications on the wood surface. (2) In chapter 5, the long-term durability investigations of the thermoset matrix, wood and composite material in artificial weathering and long-term loading scenarios with respect to the chemical surface modifications. Supporting mechanical, chemical and microstructural analyses were carried out to determine corresponding mechanisms of the bond behavior. (3) Chapter 6 presents the fire performance investigations, e.g. fire spread risk, ease of extinction and fire resistance of the matrix, CFRP and CFRP-wood. An optimization was performed based on a statistical design-of-experiments (DoE) approach. Various combinations of fire retardants were tested in different scales and differences in efficiency were analyzed. A medium-scale test setup for investigating the effectiveness of fire retardants on the fire resistance has been proposed. The mechanical analysis has validated the strength and stiffness benefits by tensile reinforcement of wood with CFRP in quasi-static conditions. The mean flexural strength and apparent modulus of elasticity of CFRP-wood was found to increase by 24 % and 53 %, respectively for small-scale samples; and by 81 % and 66 % for medium scale samples depending on the cross-section, slenderness and reinforcement ratio. The analysis of the temperature dependent dynamic mechanical response of epoxy resin, carbon fiber- reinforced polymer, wood and CFRP-wood composites in temperature ranged from -20 to 150 °C and from 0.05 to 50 Hz. The results showed that CFRP-wood had not only a significantly higher mean storage modulus of (6770 MPa at 10 °C and 0.5 Hz) compared to pure wood (5765 MPa at 10 °C and 0.5 Hz) but also retained a significantly higher portion of 92.4 % or 6253 MPa until temperatures of 95 °C than pure wood of 84.2 % or 4856 MPa, respectively. After glass transition of the epoxy matrix, the storage moduli were non-significantly different due to loss of composite action. The mean shear strength in normal conditions of 20 °C and 65 RH of epoxy-bonded spruce of 8.3 ±1.5 MPa was found to be significantly lower than the shear strength of spruce wood of 10.0 ±0.9 MPa. In A4 condition, which consisted of six hours of boiling, two hours of water storage at 20 °C and testing in wet conditions, the average shear strength of epoxy-bonded wood amounted to 5.0 ±1.2 MPa, also significantly different to spruce wood 6.7 ±0.8 MPa. Therefore, the potential improvement of bond strength could be verified. For the investigation of the long-term durability, the individual materials and composites were exposed to natural and artificial weathering conditions. The epoxy resin system was exposed to temperature, moisture and radiation under artificial weathering conditions for one, two and three months as well as under natural weathering conditions for one, three, six and nine months. The exposure effects on the polymers strength and modulus were compared to normal and hygrothermal exposure conditions. The most severe degradation was found for artificial weathering exposure due photo-oxidative processes caused by UV-intense radiation. After one month of artificial exposure to 50 °C, water spray and radiation, the mean strength amounted to 20 MPa (CV 29.3%) or 36% of the unexposed strength. The natural weathering exposure did not show significant differences in mean strength until six months. Here the mean strength of 42 MPa (CV 9.4%) was found to be 25 % lower than the reference without exposure of 56 MPa (CV 21.4%). In regards the long-term durability of CFRP-wood exposed to 20 °C and six hours of water spray per day, matrix degradation could be excluded as potential factor. Wood and CFRP-wood with and without surface modifications were tested for flexural strength and modulus of elasticity after two, four and six months exposure to 20 °C and water spray. No significant differences in mean strength 94.9 MPa (CV 6.8%) or MoE 11.1 GPa (CV 21.3%) were found for spruce wood during the exposure. Decreasing trends of both mechanical properties were observed with increasing exposure durations for all treated and untreated CFRP-wood groups. After four months of exposure, the flexural strength was statistically not significantly different from a pure wood beam of identical size, reflecting complete loss of composite action. Wood surfaces treated with peracetic acid (DEL) and octadecylchlorosilane (OTS) prior to bonding showed degradation of bond strength already at lower exposure times. The results of the OTS treatment were found to prove that the bonding behavior of epoxy and wood highly depends on the presence of hydroxyl-groups in the wood. The peracetic acid treatment, conducted to mildly delignify the woods surface in the course of increasing hydroxyl-groups was found to result in weaker bond formation between wood and epoxy resin, especially in contact with excessive moisture. An accompanying analysis with Fourier Transform Infrared spectroscopy showed that, in contrast to other delignification methods, the mild treatment did not show significant changes in the absorption in the respective wavenumbers. Hence, mild positive effects if any of the delignification on the presence of hydroxyl groups were likely to be overshadowed by decreased bond formation between wood polymers and epoxy resin due to an excess of H3O+ ions and resulting higher the energy demand for deprotonation of hydroxyl groups. The surface modification with aminopropyltriethoxysilane and dimethylformamide did not show a significant effect on the flexural strength over exposure duration compared to the untreated CFRP- wood reference. Combined with results from the epoxy resin system durability investigation, it could be shown that not bulk material degradation but degradation of the interface between epoxy and wood caused significant performance losses in CFRP-wood samples. The losses were attributed to delamination due to moisture content changes in wood of in average 9 % (CV 15.5%) and resulting stresses exceeding the wet bond strength of epoxy-bonded CFRP-wood. None of the conducted surface modifications significantly increased the durability of CFRP-wood. The fire performance of the polymer and CFRP could be significantly increased by addition of fire retardants. The design-of-experiments test approach included four fire retardants, i.e., ammonium polyphosphate (APP), aluminum trihydroxide (ATH), melamine (MEL) and expandable graphite (EG). 41 mixtures were tested in order to define the limiting oxygen index (LOI) level within the test space. A regression model was developed (R2 = 0.82) to find the maximum LOI level, which was found in the combination of 24.6 wt.-% ammonium polyphosphate (APP) and 5.4 % melamine (MEL). Due to the synergistic spumific and charring effects of both fire retardants in the epoxy matrix, the limiting oxygen index level of epoxy was increased from 21 to 45 %. In CFRP, the LOI level was increased from 26 to 41 % in carbon fiber reinforced polymers. The differences in the two materials were attributed to the mechanical hindering of the intumescent fire retardation due to the carbon fibers and wicking effect. Based on the LOI test, a selection of eighteen mixtures of polymers and CFRP were investigated in the cone calorimeter on ease of ignition and contribution to the fire. Fire retardant mixtures were found to have a significantly lower average heat release rate (HRR180s) compared to the reference. The lowest heat release rates were found for the mixture containing APP-MEL with 104 kW/m2 and APP-ATH with 98 kW/m2 were approximately one third of the reference without fire retardants with 335 kW/m2. CFRP mixtures also had significantly lower avg. heat release rates and peak heat release rates than polymer mixtures with an average difference of 24.9 % and an average difference of 20.7 % in peak heat release rate. The residual masses indicated incomplete combustion of carbon fibers during the test as opposed to thermogravimetric analysis tests with temperature range of up to 1000 °C. In comparison of LOI and cone calorimetry data on fire performance, a linear correlation with a coefficient of determination (R2) of 0.57 was found. The relatively low correlation was partly related to the fiber orientation in CFRP. Depending on it, wicking effects and mechanical hindering in the expansion of intumescent fire retardants affected the both tests to different extents. The mean tensile strength of epoxy was 55.8 MPa and significantly reduced by the incorporation of fire retardants. For APP-MEL it amounted to 29.0 MPa, for APP-ATH to 31.5 MPa and for ATH-EG retarded samples to 21.8 MPa. Although less important in CFRP due to the high strength carbon fibers, the failure strain of fire retarded epoxies also significantly decreased from 1.7 % to 0.9 % in APP-MEL, 0.8 % in APP-ATH and 0.5 % in ATH-EG retarded samples and therefore, significantly under the failure strain of carbon fibers of 1.7 %. In application, this could result in premature matrix failure while tensile strength of carbon fibers cannot be fully exploited. A medium scale test setup for investigating the effectiveness of fire retardants on the fire resistance of CFRP-wood was proposed. The effects of a 1 mm thick fire-retarded epoxy layer as fire protection of CFRP-wood was observed but due to large variances, the differences in mean time to failure or furnace temperature, respectively were not found statistically significant. Failure occurred for all specimens by a combination of delamination and wood shear failure. quickly after temperatures in the interface exceeded the glass transition temperature. Significant differences in the mean temperature in the interface between CFRP and wood were found between reference (84 °C) and fire retarded systems (APP-MEL 80.5 °C and APP-ATH 74.6 °C). The effects of fire retardants became more pronounced at longer test durations, after CFRP had delaminated, respectively.Dem Holzbau wird ein großes Potenzial zu Bewältigung der Klimakrise im Bauwesen zugeschrieben. Kohlenstoffbindung, geringer Prozessenergiebedarf und Leichtbau sind einige der Vorteile des Holzbaus, jedoch ist sein Marktanteil, insbesondere bei mehrgeschossigen Gebäuden, vergleichsweise gering. Um die Wettbewerbsfähigkeit gegenüber dem Stahlbeton- und Stahlbau zu erhöhen, versprechen Hybridmaterialien aus faserverstärkten Kunststoffen (FVK) und Holz großes Potenzial. Die Verstärkung mit einem geringen prozentualen Anteil an hochfesten und -moduligen Kohlenstofffasern kann die Gesamtfestigkeit und -steifigkeit eines Holzbauteils erheblich steigern. Als Zugbewehrung kann die Versagensart von Holzbalken von sprödem Zugversagen auf duktiles Druckversagen verändert werden. Darüber hinaus unterliegen die mechanischen Eigenschaften von Holz und Holzwerkstoffe hohen natürlichen Schwankungen, welche hohe Sicherheitsfaktoren in der Bemessung erfordern. Mit einer FVK-Verstärkung können diese Schwankungen verringert und die Verwendung von Holzwerkstoffen wirtschaftlicher werden. Eine Herausforderung stellt jedoch der Verbund zwischen dem CFK und dem Holz dar, welcher in direktem Zusammenhang mit den mechanischen Kurz- und Langzeiteigenschaften des Kompositmaterials steht. Holz, Kohlenstofffasern und duroplastische Polymere haben unterschiedliche thermische und hygrische Ausdehnungen, Elastizitäten und Festigkeiten, die unter ungünstigen Umweltbedingungen zu Delaminationen führen können. Darüber hinaus bilden die Verstärkungen zur Steifigkeitsmaximierung, sowie in nachträglicher Verstärkung durch beschränkte Zugänglichkeit bedingt, oft die äußerste Schicht von Bauteilen. Diese Stellen sind nicht nur anfälliger für Umwelteinflüsse, sondern auch für die schnelle Erhitzung im Brandfall. Die duroplastischen Matrixsysteme sind nicht nur brennbar, sondern können aufgrund ihrer niedrigen Glasübergangstemperatur im Bereich von 50 bis 150 °C auch zu einem schnellen Versagen der CFK-Verstärkung führen. Um die sichere Verwendung von CFK-Holz in der Bauindustrie zu unterstützen, sind daher zusätzliche Forschungsarbeiten erforderlich. Diese Dissertation befasst sich mit der Haltbarkeit von epoxidharzgebundenem CFK-Holz unter verschiedenen Umweltbedingungen. Das Kurzzeit-, Langzeit- und Brandverhalten von CFK-Holz wurde untersucht. Mögliche Verbesserungen durch die Modifizierung der Holzoberfläche vor der Verklebung, wie z. B. durch Grundierung mit Dimethylformamid, Silanisierung mit Aminopropyltriethoxy- und Octadecyltrichlorosilan sowie die Delignifizierung mit Peressigsäure wurden untersucht. Es wurden verschiedene Tests sowohl an den epoxid-gebundenem Holz sowie an CFK-Holz durchgeführt, einschließlich quasistatischer und dynamischer mechanischer Versuche, natürlicher und künstlicher Bewitterung und Langzeitspannungsanalysen. Unterstützende Untersuchungen umfassten chemische und mikrostrukturelle Studien der Oberfläche und des Verbunds. Die Dauerhaftigkeit in Hochtemperaturumgebungen, wie bspw. im Brandfall, wurde in kleinskaligen und Brandversuchen im Labormaßstab untersucht. Das Brandverhalten der Duroplastmatrix, des kohlenstofffaserverstärkten Polymers und des CFK-Holzes wurden analysiert und mithilfe eines statistischen Versuchsplanungsansatzes optimiert. Alle Ergebnisse wurden weiteren statistischen Analysen unterzogen, um die Signifikanz der gefundenen Effekte zu bestimmen. Der Hauptinhalt dieser Dissertation gliedert sich in drei Teile. (1) Kapitel 4 enthält die quantitative quasistatische und dynamische Analyse der Scher-, Zug- und Biegeeigenschaften der duroplastischen Matrix, des Holzes und des CFK-Holzes auf verschiedenen Skalen. Außerdem wurden unterstützende mechanische und chemische Analysen durchgeführt, um die Auswirkungen chemischer Modifikationen auf die Holzoberfläche zu bestimmen. (1) Kapitel 4 enthält die quantitative quasistatische und dynamische Analyse der Scher-, Zug- und Biegeeigenschaften der Duroplastmatrix, des Holzes und des CFK-Holzes in verschiedenen Maßstäben. Außerdem wurden unterstützende mechanische und chemische Analysen durchgeführt, um die Auswirkungen chemischer Modifikationen an der Holzoberfläche zu bestimmen. (2) In Kapitel 5 werden Untersuchungen zur Langzeitbeständigkeit der Duroplastmatrix, des Holzes und des Verbundwerkstoffs bei natürlicher Bewitterung, künstlicher Bewitterung und Langzeitbelastung unter Berücksichtigung der chemischen Oberflächenmodifikationen dargestellt. Unterstützende mechanische, chemische und mikrostrukturelle Analysen wurden durchgeführt, um die entsprechenden Mechanismen des Verbundverhaltens zu ermitteln. (3) Kapitel 6 zeigt die Untersuchungen zum Brandverhalten, wie z.B. das Brandausbreitungsrisiko, die Fähigkeit zur Selbstverlöschung und den Feuerwiderstand der Matrix, des CFK und des CFK-Holzes. Zudem wurde eine Optimierung der Brandeigenschaften auf der Grundlage eines statistischen Versuchsplans durchgeführt. Verschiedene Kombinationen von Flammschutzmitteln wurden in unterschiedlichen Maßstäben getestet und die Unterschiede in der Wirksamkeit analysiert. Es wurde ein mittelgroßer Versuchsaufbau für die Untersuchung der Wirksamkeit von Flammschutzmitteln auf die Feuerwiderstandsfähigkeit vorgeschlagen und die Wirksamkeit der identifizierten Flammschutzmixturen für CFK-Holz untersucht. Die mechanische Analyse hat die Festigkeits- und Steifigkeitsvorteile durch die Zugverstärkung von Holz mit CFK unter quasi-statischen Bedingungen bestätigt. Die mittlere Biegefestigkeit und der Elastizitätsmodul von CFK-Holz bei kleinen Proben war um 24 % bzw. 53 % und bei mittelgroßen Proben um 81 % bzw. 66 % höher im Vergleich mit unverstärktem Holz, mit Abweichungen je nach Querschnitt, Schlankheit und Verstärkungsverhältnis. Die temperaturabhängigen dynamisch-mechanischen Eigenschaften von Epoxidharz-, kohlenstofffaserverstärkten Polymer-, Holz- und CFK-Holz- Verbundwerkstoffen wurden im Temperaturbereich von -20 bis 150 °C und von 0,05 bis 50 Hz analysiert. Die Ergebnisse zeigten, dass CFK-Holz nicht nur einen signifikant höheren mittleren Speichermodul (6770 MPa bei 10 °C und 0,5 Hz) im Vergleich zu reinem Holz (5765 MPa bei 10 °C und 0,5 Hz) aufweist, sondern auch einen signifikant höheren Anteil von 92,4 % bzw. 6253 MPa bis zu Temperaturen von 95 °C beibehält als reines Holz mit 84,2 % bzw. 4856 MPa. Nach dem Glasübergang der Epoxidmatrix unterschieden sich die Speichermodule aufgrund des Verlustes der Verbundwirkung nicht mehr signifikant. Die mittlere Scherfestigkeit von epoxidgebundenem Fichtenholz unter normalen Bedingungen (20 °C und 65 RH) war mit 8,3 ±1,5 MPa deutlich niedriger als die longitudinale Scherfestigkeit von Fichtenholz mit 10,0 ±0,9 MPa. Unter Exposition nach A4, d.h. sechs Stunden Kochen, zwei Stunden Wasserlagerung bei 20°C und anschließender Prüfung unter nassen Bedingungen betrug die durchschnittliche Scherfestigkeit von epoxidgebundenem Holz 5,0 ±1,2 MPa, ebenfalls ein signifikanter Unterschied zu Fichtenholz mit 6,7 ±0,8 MPa. Ein mögliches Verbesserungspotenzial in der Verbundfestigkeit wurde somit identifiziert. Für die Untersuchung der Langzeitbeständigkeit wurden die einzelnen Materialien und Verbundwerkstoffe natürlichen und künstlichen Bewitterungsbedingungen ausgesetzt. Das Epoxidharzsystem wurde unter künstlichen Bewitterungsbedingungen für einen, zwei und drei Monate sowie unter natürlichen Bewitterungsbedingungen für einen, drei, sechs und neun Monate Temperatur, Feuchtigkeit und UV-Strahlung ausgesetzt. Die Auswirkungen der Exposition auf die Festigkeit und den Modul des Polymers wurden mit normalen und hygrothermischen Expositionsbedingungen verglichen. Die stärkste Minderung wurde bei bei künstlicher Bewitterung durch photooxidative Prozesse festgestellt, die durch intensive UV-Strahlung verursacht wurden. Nach einem Monat künstlicher Bewitterung bei 50 °C, Wassersprühens und Bestrahlung betrug die mittlere Festigkeit noch 20 MPa (CV 29,3 %) oder 36 % der Festigkeit vor Exposition. Die natürliche Bewitterung zeigte bis zu sechs Monaten keine signifikante Auswirkung auf die mittlere Festigkeit. Erst nach sechs Monaten lag die mittlere Festigkeit mit 42 MPa (CV 9,4 %) um 25 % signifikant niedriger als die Referenz ohne Bewitterung mit 56 MPa (CV 21,4 %). In Bezug auf die Langzeitbeständigkeit von CFK- Holz, das 20 °C und s
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
Global tidal mapping from observations of a radar campaign
No full textAbstract not availableYou Yu, Weixing Wan, Iain M. Reid, Jinsong Chen, Robert A. Vincent, Baiqi Ning, Damian J. Murphy, Guotao Yang, Xianghui Xue, Andrew D. MacKinnon, Na Li, Chunxiao Yan, Libo Liu, Lianhuan Hu, Zhipeng Ren, Yun Zhan
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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