1,721,030 research outputs found
Analytical three-body interaction potentials and hydrogen bond dynamics of hydrogen fluoride aggregates, (HF)(n), n >= 3
No full textOligomeric aggregates of hydrogen fluoride are important prototype molecules for a detailed understanding of the structure, energetics, spectroscopy and dynamics of hydrogen bonding. The pairwise additive description of these oligomers is known to be inadequate. We have sampled the three-body potential for HF at 3000 (HF)(3) configurations selected by various classical and quantum sampling techniques, including dynamic sampling based on Voronoi step representation. The counterpoise-corrected Moller-Plesset second-order three-body energies using a double zeta Gaussian basis set with polarization functions (DZP + MP2) at these configurations are fitted by analytical 12-dimensional potentials. Cooperative effects are found to be sizeable and predominantly stabilizing in hydrogen fluoride ring aggregates. Test calculations with larger basis sets and for larger HF aggregates show that in combination with available high quality pair potentials, the analytical three-body terms give an excellent description of the (HF)(3) surface in the hydrogen bonding region and a good approximation for clusters up to at least the hexamer. Multidimensional vibrational quantum Monte Carlo calculations indicate that degenerate HF stretch excitation in (HF)(3) (3712 cm(-1)) is in close coincidence with (HF)(3) --> 3HF dissociation channels at low HF angular momentum, whereas degenerate DF stretch excitation in (DF)(3) (2725 cm(-1)) falls slightly below any (DF)(3) --> (DF)(2) + DF dissociation channels. The (HF)(3) potential surface, its stationary points, possible interconversion tunneling pathways, zero point energies, adiabatic channels, unusual isotope effects, fully centrifugal rotational states and the harmonic infrared spectrum are discussed in detail and compared to ab initio calculations and experiment. The applicability of the (1 + 2 + 3)-body approach for larger oligomers (3 < n < 8) is investigated with special emphasis on structure, energetics, infrared and microwave spectra, and predissociation. Neglect of four- and higher-body contributions and hydrogen exchange symmetry is found to affect some properties significantly, but the preference for simple ring structures remains pronounced. (C) 2001 Elsevier Science B.V. All rights reserved
Autonomous Airborne Wind Energy Systems: Accomplishments and Challenges
No full textAirborne wind energy (AWE) is a fascinating technology to convert wind power into electricity with an autonomous tethered aircraft. Deemed a potentially game-changing solution, AWE is attracting the attention of policy makers and stakeholders with the promise of producing large amounts of cost-competitive electricity with wide applicability worldwide. Since the pioneering experimental endeavors in the years 2000-2010, there has been a clear technology convergence trend and steady progress in the field. Today, AWE systems can operate automatically with minimal supervision in all operational phases. A first product is also being commercialized. However, all-around fully autonomous operation still presents important fundamental challenges that are conceptually similar to those of other systems that promise to change our lives, such as fully autonomous passenger cars or service drones. At the same time, autonomous operation is necessary to enable large-scale AWE, thus combining challenging fundamental problems with high potential impact on society and the economy. This article describes the state of the art of this technology from a system perspective and with a critical view on some fundamental aspects, presents the latest automatic control results by prominent industrial players, and finally points out the most important challenges on the road to fully autonomous AWE systems
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
GRUNDSÄTZE UND EMPFEHLUNGEN ZUR WAHRUNG UND FÖRDERUNG DER WISSENSCHAFTSFREIHEIT IN DEUTSCHLAND
No full textAsh MG, Quack M, Gläser J, et al., eds. GRUNDSÄTZE UND EMPFEHLUNGEN ZUR WAHRUNG UND FÖRDERUNG DER WISSENSCHAFTSFREIHEIT IN DEUTSCHLAND. Wissenschaftspolitik im Dialog. 2024;25
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
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