1,720,958 research outputs found
Centerband‐Only Detection of Exchange NMR with Natural‐Abundance Correction Reveals an Expanded Unit Cell in Phenylalanine Crystals
No full textAbstract The NMR pulse sequence CODEX (centerband‐only detection of exchange) is a widely used method to report on the number of magnetically inequivalent spins that exchange magnetization via spin diffusion. For crystals, this rules out certain symmetries, and the rate of equilibration is sensitive to distances. Here we show that for 13C CODEX, consideration of natural abundance spins is necessary for crystals of high complexity, demonstrated here with the amino acid phenylalanine. The NMR data rule out the C2 space group that was originally reported for phenylalanine, and are only consistent with a larger unit cell containing eight magnetically inequivalent molecules. Such an expanded cell was recently described based on single crystal data. The large unit cell dictates the use of long spin diffusion times of more than 200 seconds, in order to equilibrate over the entire unit cell volume of 1622 Å3.NMR crystallography with CODEX: hundreds of seconds of spin diffusion are used to detect the eight molecules in a large unit cell. Encoded chemical shift anisotropy reveals information hidden in the isotropic spectrum. Accuracy requires correction for natural‐abundance spins in the single‐site carbon‐13‐labelled sample. imageDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Max-Planck-Gesellschaft http://dx.doi.org/10.13039/50110000418
Helical Fibers via Evaporation‐Driven Self‐Assembly of Surface‐Acylated Cellulose Nanowhiskers
No full textMany natural materials have helical or twisting shapes. Herein, we show the formation of helical fibers with the lengths of micrometers by the evaporation‐driven self‐assembly on silicon wafers of functionalized cellulose nanowhiskers (CNWs) with surface‐attached acyl chains. The self‐assembly process and the final helical structures were affected by parameters including the wettability of substrates, dispersing solvents, the amount of 10‐undecenoyl groups, the crystallinity, the dimension of CNWs, and the length of acyl chains. In particular, surface‐acylated CNWs with a certain amount of 10‐undecenoyl groups (ca. 3.52 mmol g−1), an appropriate crystallinity (ca. 40 %), a length of about 135 nm, and a diameter of around 4 nm, preferentially self‐assembled into explicit left‐handed helical fibers from their THF suspensions on wafers. Thus, we showed novel particular self‐assembly behaviors of surface‐acylated CNWs, and we expanded the materials spectrum for the construction of helical structures
Protein-Drug Interactions in the Membrane: The Small Molecule Anle138b and its Binding to α-Synuclein Oligomers
No full text
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
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