1,721,405 research outputs found
Zwitterionic Systems Obtained by Condensation of Heteroaryl-Boronic Acids and Rhodizonic Acid
No full textThe boronic acid derivatives 4-pyridinylboronic acid (4-pyBA) and pyrimidine-5-boronic acid (pyrBA) have been reacted with the oxocarbon rhodizonic acid or with sodium rhodizonate both in solution and in the solid state. Four novel condensation adducts have been isolated as hydrates, namely C16H16B2N2O12•xH2O (1a•xH2O; x = 2 or 4), C16H14B2N2O10•3H2O (2a•3H2O), C14H14B2N4O12•2.5H2O (1b•2.5H2O), and C14H12B2N4O10•3H2O (2b•3H2O), and fully characterized by X-ray single crystal and powder diffraction. Their thermal stability and behavior upon dehydration have also been investigated by TGA and single-crystal to single-crystal X-ray diffraction experiments. It has been shown that the boronic acid derivatives 4-pyridinylboronic acid and pyrimidine-5-boronic acid react with rhodizonic acid in a similar way producing two distinct products, the so-called “axle” compounds (1a and 1b) and “tweezer” compounds (2a and 2b), depending on the experimental conditions and preparation method. With both boronic acids, the “tweezer” compound is the only product of the mechanical mixing of the reactants. Both “axle” and “tweezer” compounds are in the zwitterionic form with the boronate ion being neutralized via protonation on the pyridinyl and pyrimidine N-terminus
Partial discharge measurements in electrical machines controlled by variable speed drives: From design validation to permanent PD monitoring
No full textThe evolution of IEC 60034-18-41 from technical specification to standard: Perspectives for manufacturers and end users
No full textThe document IEC 60034-18-41 for inverter-fed rotating machines is undergoing a radical revolution: born as a technical specification, it is going to become a standard. One of the points that will influence most strikingly machine manufacturer-customer relations is the concept of impulse rated voltage (IRV): a quantity that will be printed on the machine nameplate and needs to be explained. Also, as wire-wound insulation systems are qualified or not depending on partial discharges measurements, it is vital to face the challenges of partial discharge detection under repetitive surge voltages. According to the above, this paper will first summarize the main features of the IEC 60034-18-41 document. After that, a short description of a system able to detect partial discharge under repetitive voltage surges and its applications will be presented
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
Precessional Motion in Crystalline Solid Solutions of Ionic Rotors
No full textThe order–disorder phase transition associated with the uprise of reorientational motion in (DABCOH2)2+, in the supramolecular salts of general formula [1·(DABCOH2)]X2 (where 1=12-crown-4, DABCO=1,4- iazabicyclo[2.2.2]octane, and X=Cl- or Br-), has been investigated by variable temperature X-ray diffraction on single crystals and powder samples, as well as by DSC and solid-state NMR spectroscopy (SSNMR). The two compounds undergo a reversible phase change at 292 and 290 K, respectively. The two crystalline materials form solid solutions [1·(DABCOH2)]Cl2xBr2(1-x) in the whole composition range (0 < x<1), with a decrease
in the temperature of transition to a minimum of ca 280 K, corresponding to x=0.5. Activation energy values for the dynamic processes, evaluated by variable-temperature 13C magic-angle spinning (MAS) SSNMR and line-shape analysis are ca. 50 kJmol-1 in all cases. Combined diffraction and spectroscopic evidence has allowed the detection of a novel dynamic process for the (DABCOH2)2+ dications, based on a room temperature precessional motion that is frozen out below the disorder–order transition; to the best of the authors’ knowledge this phenomenon has never been observed before
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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