1,721,001 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
Volatility homogenisation and machine learning for time series forecasting
No full text© 2016 Dr. Adam Waldemar KowalewskiVolatility homogenisation is a technique of looking at a process at regular points in space. In other words, we are only interested when the process moves by a certain quantum. The intuition and empirical evidence behind this is that we ignore smaller movements which are just noise, while only concerning ourselves with larger movements which represent the information from the underlying process. In this vein, we have derived theoretical results showing volatility homogenisation as a means of estimating the drift and volatility of theoretical processes and verify these results by simulation. This demonstrates the ability of a “homogenised” process to retain salient information regarding the underlying process.
Volatility homogenisation is then coupled, as a preprocessing step, with various machine learning techniques which yields greater forecasting accuracy than when the machine learning techniques are used without volatility homogenisation preprocessing. In addition to this, we develop volatility homogenisation kernels for machine learning kernel-based techniques such as support vector machines, relevance vector machines and Gaussian processes for machine learning. The volatility homogenisation kernel causes a kernel-based machine learning technique to utilise volatility homogenisation internally and, with it, obtain better predictions on forecasting the direction of a financial time series. In order to create and use the volatility homogenisation kernel, we have developed a solution to the problem of a kernel taking inputs which have dimensions of differing size while still maintaining a convex solution to the model for techniques such as support vector machines, for a given set of parameters.
Furthermore, we have demonstrated the efficacy of volatility homogenisation as a way of successfully investing using a Kelly criterion strategy. The strategy makes use of the information inherent in a support vector machine model which uses a volatility homogenisation kernel in order to calculate the necessary parameters for the Kelly betting strategy. We also develop strategies which select additional features for the support vector machine through the use of a nearest neighbour strategy using various measures of association.
Overall, volatility homogenisation is a robust strategy for the decomposition of a process which allows various machine learning techniques to discern the main driving process inherent in a financial time series, which leads to better forecasts and investment strategies
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
Stereochemical Memory in the Temperature-Dependent Photodenitrogenation of Bridgehead-Substituted DBH-Type Azoalkanes: Inhibition of Inverted-Housane Formation in the Diazenyl Diradical through the Mass Effect (Inertia) and Steric Hindrance
No full textThe photochemical denitrogenation of the cyclopentene-annelated DBH-type azoalkanes 1 has been examined in solution as a function of bridgehead substitution and temperature. For all derivatives, namely, the unsubstituted 1a(H/H), monomethyl 1b(Me/H) dimethyl 1c(Me/Me), monophenyl 1d(Ph/H), and diphenyl 1e(Ph/Ph), the temperature-dependent ratio of syn and anti housanes 2 provides experimental support for a competition between the singlet (high temperature) and triplet (low temperature) reaction channels in the direct photolysis. The syn/anti ratio of the housanes 2 depends on the extent and type of bridgehead substitution; the amount of the anti diastereomer (retention) follows the order Ph > Me > H, and double substitution is more effective than single. This stereochernical memory is interpreted in terms of the mass effect (inertia) of the substituents and steric interaction (size) between the substituents at the bridgehead and the methylene bridge during the deazetation step of the transient diazenyl diradical conformations (1)DZ (exo-ax) and (1)DZ (exo-eq). These conformers are impulsively generated upon decay of the (1)(n,pi*)-excited azoalkane, a trajectory assessed through computational work. The new mechanistic feature disclosed by the unprecedented anti stereoselectivity (retention) is the intervention of a puckered 1,3-cyclopentanediyl singlet diradical (DR)-D-1 as product bifurcation step, whose conformational relaxation to the planar species (loss of stereochernical memory) is encumbered by bridgehead substitution
The Thermal Decomposition of 1,2-Dioxetane Revisited
No full textThe ground state (S0) and lowest energy triplet state (T1) energy surfaces of the parent dioxetane have been extensively explored using various CASSCF active spaces with MP2 corrections in several basis sets. In particular, the singlet/triplet surface crossing regions have been examined and the spin - orbit coupling and energetics computed. The computed energy barrier for the ring-opening of dioxetane is 16 kcal mol-1, which is lower than the experimentally observed threshold (22 kcal mol-1) for unsubstituted dioxetane decomposition. However, the surface topology is in good agreement with the experimental observations. The barrier for O - O cleavage on the ground state surface is found to lie at nearly the same energy as the transition structure for C - C biradical cleavage on the triplet energy surface. More significantly, the computational results indicate that the singlet and triplet surfaces do not cross along the minimum energy path (MEP) between the ground state O - O cleavage transition state and the singlet biradical. as previously thought. Instead, the S0 → 3(3π) surface crossing is prompted by a motion orthogonal to the reaction coordinate, which has components along both the OC - CO torsional and O - C - C asymmetric bending vibrational modes. In particular, we find evidence for a singlet/triplet crossing "line" that spans the ground state O - O cleavage valley and lies a few kcal mol-1 higher in energy. The computed spin - orbit coupling between the ground state and triplet 3(3π) surfaces is large (ca. 60 cm-1) throughout this crossing region. Therefore it is suggested that facile intersystem crossing (ISC) from the ground state to the triplet surface can occur anywhere along the MEP. ISC leads to production of a .OCH2 - CH2O. triplet biradical that can either fragment to form triplet products or undergo ISC back to the ground state surface. The existence of a triplet/singlet crossing region located very close to the computed triplet biradical, suggests that this species is metastable with a short (picosecond) lifetime
Theoretical Study of the 1,2 Rearrangement of Housane Radical Cations: Key Role of a Transient Cyclopentane-1,3-diyl Intermediate
No full textCASSCF computations suggest that the ground-state potential energy surface of housane radical cations is centered around a conical intersection (and its surrounding Jahn-Teller-type surface) at a planar, symmetric cyclopentane-1,3-diyl geometry. In our reactivity model, this region is connected to the reactants via a bridge-bending coordinate and to the products via a shift coordinate. The preference for the spin-localized planar intermediate is caused by the preferential energy stabilization along a charge localization coordinate (the derivative-coupling coordinate at the conical intersection). Mechanistically, our computations show that the reaction proceeds in two steps: the breakage of the one-electron bond of the reactants, which produces the asymmetric, quasi-planar intermediate and is the rate-determining step, and the subsequent 1,2 rearrangement, which is essentially barrierless. The reaction results in the selective 1,2 migration of the original endo substituent of the reactant
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