1,720,974 research outputs found
Ab-Initio Study of Model Guanosine Assemblies: the Role of pi-pi Coupling and Band Transport
No full textSeveral assemblies of guanine molecules are investigated by means of first-principles calculations. Such structures include stacked and hydrogen-bonded dimers, as well as vertical columns and planar ribbons, respectively, obtained by periodically replicating the dimers. Our results are in good agreement with experimental data for isolated molecules, isolated dimers, and periodic ribbons. For stacked dimers and columns, the stability is affected by the relative charge distribution of the pi orbitals in adjacent guanine molecules. pi-pi coupling in some stacked columns induces dispersive energy bands, while no dispersion is identified in the planar ribbons along the connections of hydrogen bonds. The implications for different materials comprised of guanine aggregates are discussed. The band structure of dispersive configurations may justify a contribution of band transport (Bloch type) in the conduction mechanism of deoxyguanosine fibres, while in DNA-like configurations band transport should be negligible
A study of the structure of the lyomesophases formed by the dinucleoside phosphate d(GpG). An approach by X-ray diffraction and optical microscopy
No full textG-Quartet Biomolecular NanoWires
No full textWe present a first-principle investigation of quadruple helix nanowires, consisting of stacked planar hydrogen-bonded guanine tetramers. Our results show that long wires form and are stable in potassium-rich conditions. We present their electronic band structure and discuss the interpretation in terms of effective wide-band-gap semiconductors. The microscopic structural and electronic properties of the guanine quadruple helices make them suitable candidates for molecular nanoelectronics. (C) 2002 American Institute of Physics
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
Sequence specificity of psoralen photobinding to DNA: a quantitative approach
No full textThe effect of different DNA sequences on the photoreaction of various furocoumarin derivatives was investigated from a quantitative poin of view using a number of selfcomplementary oligonucleotides. The furocoumarins included classical bifunctional derivatives, such as 8-methoxy and 5-methoxypsoralen, as well as monofunctional compounds, such as angelicin and benzopsoralen. This approach, in combination with footprinting studies, appears to be quite useful for a quantitative investigation of the process of covalent binding of psoralens to specific sites in DNA
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
Assignment of phosphate groups and determination of P,H coupling constants in the DNA fragment d(CGTACG) by31P 2D NMR experiments
No full text2D 31P/1H correlation spectroscopy has been used to assign individual phosphates in the self-complementary DNA fragment d(CGTACG), which is present in solution as a B-DNA type double helix. 31P chemical shift variation with temperature and with the base sequence has been studied, and evidence is given of a steric clash between purines in the minor groove, affecting the chemical shift of the innermost TpA phosphate. For this hexanucleotide there is a good correlation of 31P shifts with both the helical twist (∑1) and roll angle (∑2) Calladine-Dickerson sum functions. Different types of linear correlations, also including data from other nuclotides, have been performed. The results show that it is more appropriate to consider the change in chemical shifts as it occurs during melting rather than the actual 31P shifts. An interesting correlation was also found between 31P chemical shifts and P,H-3′ coupling constants
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
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