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PS2.M: Looking for a potassium biosensor
No full textDNA sequences with guanine repeats are able to fold as G-quadruplex (G4) structures. This is an alternative DNA conformation in which four guanines are arranged as a tetrad, the structural unit of G4; two or more stacked tetrads form a G4 structure. The hydrogen bonds characterizing G4 are called Hoogsten bonds but more interactions are involved in the G4 structure stabilization. For example, cations work as G4 stabilizers and their role is not restricted to the structural folding. They coordinate the guanines’ carbonilic oxygens located towards the hydrophobic channel of the G4 inner structure. This feature suggests that the G4 could work as a cation biosensor. Biological media are characterized by the simultaneous presence of K+and Na+exhibiting different affinities and thus promoting different topological arrangements in the folding solution. In this article we explore the possibility of using PS2.M, an 18 base long synthetic oligonucleotide, as a detector of K+at concentrations in the range 0mM to 10mM. Our intent is therefore to study a biosensor that is made of the G4 sequence only, without intervention of other coupled molecules. As with most guanine-rich oligonucleotides, also PS2.M shows different structures depending on the folding conditions. In agreement with the literature data, our results outline the expected behavior and the key role of K+and Na+in promoting the folding, with Na+promoting the antiparallel structure formation of PS2.M, even at high concentrations. On the other hand, if PS2.M is folded in 10mM to 100mM KCl solutions, the parallel conformation sets in becoming more and more relevant as concentration grows. In a complex solution of G4 in the presence of both K+and Na+ions, spectra display the coexistence of parallel, antiparallel and mixed type conformations. Results show that the CD spectra values at this wavelength can be diagrammed as a function of the K+concentration to construct a biosensor calibration curve. In conclusion, given a Na+concentration in the range 50mM to 80mM and K+concentration in the range 0mM to 10mM, the measured CD signal at 263.6nm permits a K+concentration measurement with a resolution of ∼ 1 mM
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
MDI: integrity index of cytoskeletal fibers observed by AFM
No full textThe Modified Directional Index (MDI) is a form factor of the angular spectrum computed from the 2D Fourier transform of an image marking the prevalence of rectilinear features throughout the picture. We study some properties of the index and we apply it to AFM images of cell cytoskeleton regions featuring patterns of rectilinear nearly parallel actin filaments as in the case of microfilaments grouped in bundles. The analysis of AFM images through MDI calculation quantifies the fiber directionality changes which could be related to fiber damages. This parameter is applied to the images of Hs 578Bst cell line, non-tumoral and not immortalized human epithelial cell line, irradiated with X-rays at doses equivalent to typical radiotherapy treatment fractions. In the reported samples, we could conclude that the damages are mainly born to the membrane and not to the cytoskeleton. It could be interesting to test the parameter also using other kinds of chemical or physical agents
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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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