1,721,008 research outputs found
Stability of wide-graded rubble mounds
Full text linkThe reshaping of temporary rubble mounds like the core of breakwaters or reclamation bunds is often a concern for contractorsi n the construction stages of marine structures. The formulas found in literature for the prediction of such behavior are few, and they do not provide clear insight on the influence of relevant parameters, in particular the small dimensions and wide stone-size gradation of the material involved, usually consisting of quarry run or resulting from dredging. The previous research in the field of dynamic stability focused on berm breakwaters and gravel beaches. These two typologies of structures define the range to which the rubble mounds considered in this study generally belong. An overview on the design tools provided by the technical literature shows that, whenever the grading was included as a governing parameter, some influence was recognized in the characteristics of the structure (e.g. the permeability) and in the dynamism of the different fractions of stone sizes. However, very wide ranges of the parameter grading were never investigated and a specific analysis in this direction constitutes the main significance of this study. The Delft University of Technology provided the laboratory facilities to carry out physical model tests on a wide graded rubble mound structure representative of the core of a breakwater. The parameter D85/D15, describing the stone-size gradation of the construction material, was varied between the values 2.71 and 17.7, and two different seaward slopes of the model structure were also tested. The reshaped cross-shore profiles measured during the tests showed how if the grading increases the stability of the structure is reduced. This is not always in accordance with the findings of previous researchers, showing how the extrapolation of existing empirical formulas to structures with high values of the ratio D85/D15 do not give reliable results. Instead, the formulas given by van de Meer (1992) to estimate the whole reshaped profile of a dynamic slope predict with good agreement the shape of the measured profiles, although the physical model shows a larger horizontal extension of the displacements. This difference is governed by the grading, being more noticeable as this parameter increases. This result leads to the definition of new formulas, some of them being modifications of the ones given by van der Meer, to describe the geometry of a reshaped profile. The formulas, all including the parameter grading, are derived through curve fitting of the measured data. Also a formula for the direct estimation of the crest recession is given. As a final step, a simple numerical model is proposed in which the new formulas are implemented, constituting a quick way to assess the shape of a slope after a wave attack. As a suggestion for further utilization of the results of physical modeling, a brief comparison is also carried out between the output of the tests and the prediction of the numerical model XBeach (developed mainly at UNESCO-IHE). In conclusion, this research points out how the formulas provided by the technical literature are not reliable in representing the effects of a very wide stone-size gradation in the stability of a rubble mound structure. Physical model tests proved to be a suited way to investigate these effects, as the nature of the phenomena who play a role in the stability does not allow a simple analytical representation. The tests carried out within the present study lead to the implementation of a numerical model of practical use for engineers and contractors: further investigations through laboratory tests are recommended to validate and extend the findings of this study. Another proposed direction for further research is the comparison between the results of physical model tests and the output of numerical models.Hydraulic EngineeringCivil Engineering and Geoscience
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
From smart drugs to smartphone: A colorimetric spot test for the analysis of the synthetic cannabinoid AB-001
No full textVisible Light Uranyl Photocatalysis: Direct C–H to C–C Bond Conversion
No full textUranyl nitrate hexahydrate performs as an efficient photocatalyst in the direct C–H to C–C bond conversion under blue light irradiation via hydrogen atom transfer (HAT). This uranyl salt enables the remarkable smooth functionalization of unactivated (cyclo)alkanes, ethers, acetals, and amides via radical addition onto electrophilic olefins. Dedicated electrochemical measurements on compounds and intermediates involved in the process were carried out to support the mechanistic proposal
Electrochemical analysis and characterization of psychoactive substances glaucine and tetrahydropalmatine
No full textThe electrochemical behaviour of two alkaloids of forensic interest, namely glaucine and tetrahydropalmatine, has been investigated by Cyclic Voltammetry (CV) and Controlled Potential Electrolysis (CPE) and the results compared with those obtained with model compounds such as tetrahydroisoquinolines and methoxybenzenes. On the basis of these results, we developed an analytical procedure based on differential pulsed voltammetry (DPV), associated with a clean-up/preconcentration process by solid phase extraction (SPE) using Florisil, that can be applied for the detection and quantification of the analytes both in pharmaceutical preparations and in biological matrices such as urines. LOD values around 0.15 μg∙mL−1 and linearity up to 250 μg∙mL−1 were measured
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