1,721,148 research outputs found
Aromatic and antiaromatic ring currents in a molecular nanoring
Full text linkThis dataset accompanies the publication: M. D. Peeks, T. D. W. Claridge and H. L. Anderson, âAromatic and antiaromatic ring currents in a molecular nanoringâ, Nature, 2017, http://dx.doi.org/10.1038/nature20798 . The associated publication describes the aromaticity and antiaromaticity of a [6]-porphyrin nanoring as a function of the oxidation state of the nanoring. At the time of publication, these were the largest (anti)aromatic systems reported. The diameter of the [6]-porphyrin nanoring is 2.4 nm. The contents of this supporting dataset are described in the âDATA MAP.txtâ file
Anomalous nuclear overhauser effects in carbon-substituted aziridines: Scalar cross-relaxation of the first kind
Full text linkAnomalous NOESY cross-peaks that cannot be explained by dipolar cross-relaxation or chemical exchange are described for carbon-substituted aziridines. The origin of these is identified as scalar cross-relaxation of the first kind, as demonstrated by a complete theoretical description of this relaxation process and by computational simulation of the NOESY spectra. It is shown that this process relies on the stochastic modulation of J-coupling by conformational transitions, which in the case of aziridines arise from inversion at the nitrogen center. The observation of scalar cross-relaxation between protons does not appear to have been previously reported for NOESY spectra. Conventional analysis would have assigned the cross-peaks as being indicative of a chemical exchange process occurring between correlated spins, were it not for the fact that the pairs of nuclei displaying them cannot undergo such exchange. Scalar relaxation: Apparently anomalous cross-peaks in 2D 1HNOESY spectra of carbon-substituted aziridines are shown to arise from scalar cross-relaxation of the first kind (SRFK; see picture), due to modulation of scalar coupling constants between protons. Such effects will likely be seen in NOESY spectra of other small molecules experiencing dynamic exchange modulation of scalar 1H-1H coupling constants
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
Scalar cross-relaxation detected in the NOESY spectra of oxazolidines and thiazolidines
Full text linkAnomalous cross-peaks observed in the NOESY spectra of 2,4-disubstituted thiazolidines and oxazoli-dines that cannot be attributed to classical dipolar NOE or chemical exchange peaks have been investi-gated experimentally and computationally and shown to arise from scalar cross-relaxation of the first kind (SCRFK). This process is stimulated by the relatively slow modulation of scalar couplings, and for the systems studied arises from slow on-off proton exchange of the amino nitrogen, a process influenced by solution temperature, acidity and concentration. The mechanism is likely to be significant for many systems in which proton exchange occurs on the millisecond timescale, and misinterpretation of these cross-peaks may lead to erroneous conclusions should their true origins not be recognised
Measuring spin relaxation rates using satellite exchange NMR spectroscopy
Full text linkAn approach to the indirect measurement of nuclear spin relaxation rates of low‐magnetogyric ratio (γ) nuclei using the process of satellite exchange is described. The method does not require the observation of, or even the ability to provide radio‐frequency pulses to, the low‐γ nucleus, but requires this to be scalar coupled to an NMR observable nucleus, such as 31P or 1H, making it especially attractive for the study of diamagnetic transition metals. In situations where spin relaxation is dominated by chemical shift anisotropy (CSA), the determination of the longitudinal spin relaxation time constant (T1) of the metal becomes possible, as illustrated for 195Pt and 107/109Ag
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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