1,720,958 research outputs found
Dicopper Double-Strand Helicates Held Together by Additional π–π Interactions
No full textThe bis-bidentate ligand, obtained from Schiff base
condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L−L), forms with [CuI (MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π−π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The
[CuI2(L−L)2]2+ complex, which does not decompose even on excess addition of either L−L or CuI, undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [CuICuII(L−L)2]3+ with respect to disproportionation to [CuI
2(L−L)2]2+ and [CuII2(L−L)2]4+ is essentially due to a favorable electrostatic term. CuII forms with L−L a stable species, with a 1:1 stoichiometric ratio,but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. However, CV studies on an MeCN solution containing equimolar amounts of CuII and L−L showed the presence in the reduction scan of two
fully reversible waves, separated by about 250 mV, which indicated the presence in solution of a dicopper(II) double strand helicate complex, [CuII2(L−L)2]4+. This work demonstrates that additional interstrand π−π interactions can favor the formation of unusually stable dicopper(I) and dicopper(II) helicate complexes
Octahedral Copper(II) and Tetrahedral Copper(I) Double-Strand Helicates: Chiral Self-Recognition and Redox Behavior
No full textThe racemic form of the linear multidentate ligand L (RRL þ SSL) gives dinuclear complexes of 2:2 stoichiometry both with CuII, acting as a bisterdentate
ligand, and with CuI, acting as a bis-bidentate ligand. Single crystal X-ray diffraction studies have shown that
the CuII complex exists as double-strand homochiral helicate molecules: P,P-[Cu2
II(RRL)2]4þ and M,M-[Cu2
II-
(SSL)2]4þ; in which the two trans-1,2-cyclohexanediamine subunits have the same chirality for of the two strands.
Each CuII metal center is six-coordinated according to a cis-octahedral geometry and interacts with a NNO donor
subunit of each strand. The CuI complex, when crystallized from THF in the presence of racL, gives a double-strand
homochiral helicate complex and in the solid state forms a racemic mixture of the homochiral metal complexes M,
M-[Cu2
I(RRL)2]2þ and P,P-[Cu2
I(SSL)2]2þ. When crystallizing from a MeCN solution, CuI and racL give rise to the
heterochiral nonhelicate dimeric complex [Cu2
I(RRL)(SSL)]2þ, in which the two strands of the dimer have inverse
configuration of the trans-1,2-cyclohexanediamine subunits and are assembled side-by-side. In both structural
architectures, the CuI centers are four-coordinated by two nitrogen atoms from each strand, according to a distorted
tetrahedral geometry. In MeCN solution, the dinuclear CuII complex disassembles to give the mononuclear species,
which, on reduction at a platinum electrode in a cyclic voltammetry experiment, gives two CuI mononuclear complexes
that quickly assemble to give the dinuclear CuI complex. This complex undergoes two consecutive one-electron
oxidation processes, but the dinuclear CuII species that forms decomposes in less than 1 s. On the contrary, the
[Cu2
I(racL)2]2þ complex is stable in MeCN solution and undergoes two one-electron oxidation processes to give a form
of dinuclear CuII complex that lasts in solution for more than 20 s
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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