1,721,129 research outputs found
A polarized-light spectroscopy study of interactions of a hairpin polyamide with DNA
No full textWe here study the interactions of a polyamide with large DNA, and compare to those of minor groove binder distamycin (DST), including high ligand/DNA binding ratios. Specific as well as nonspecific binding is probed using polarized-light spectroscopy combined with singular value decomposition analysis. Circular and linear dichroism data confirm binding geometries consistent with minor groove binding for both of the ligands. Interestingly, at high and intermediate ligand/DNA ratios the polyamide exhibits no significant sequence discrimination between mixed-sequence (calf thymus) and AT DNA as compared to DST. Each ligand is concluded to exhibit two different binding modes depending upon ligand/DNA ratio and nucleo-base sequence. At high binding ratios, distinct differences between the ligands are observed: circular dichroism spectra exciton effects provide evidence of bimolecular interactions of the polyamide when bound to AT-DNA, whereas no effects are seen with DST or mixed-sequence DNA. Also linear dichroism indicates that a change in binding geometry occurs at high polyamide/AT ratios, and that the effect occurs only with polyamide in contrast to DST. Since the effect is insignificant with DST, or with calf thymus DNA, it is concluded that it relates to the sizes of the ligands and the minor grooves, becoming critical in the limit of crowding
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
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
Synthetic analogs of sialyl Lewis x
No full textThe sialyl Lewis x (SLex) tetrasaccharide is the smallest recognizable ligand for selectins. The selectins constitute a vital part of the inflammatory cascade for recruitment of leukocytes to a site of tissue damage or microbial infection. If too many leukocytes are recruited, normal, not injured, cells can be damaged; a process known from chronic inflammatory diseases such as reumatoid arthritis, psoriasis, and from septic shock and reperfusion damage. Sialyl Lewis x saccharides were originally identified as human tumor-associated antigens and are found on all highly malignant types of cancer cells. The identification of the SLex tetrasaccharide and later synthetic efforts have elucidated the biologically important features of the molecule. A large number of analogs and mimics have been designed in order to get simpler and more stable compounds for use as anti-inflammatory drugs. Sialic acid-containing oligosaccharides, such as sialyl Lewis x, can form lactones under slightly acidic conditions. These lactones are generally more immunogenic due to their increased rigidity and it has been proposed that the lactones are the actual immunogens. The lactones are however not hydrolytically stable and are therefore difficult to investigate and to raise antibodies against. Lactams were introduced as analogs to lactones and were found to be structurally similar and more stable against hydrolysis. Lactam analogs of a number of monosialylated gangliosides (GM2, GM3, GM4) were synthesized and used with success. This thesis describes the synthesis of the sialyl Lewis x tetrasaccharide, the Lewis x trisaccharide, the 1’’’-2’-, 1’’’-4’-lactam- and 2-acetamido analogs of the sialyl Lewis x tetrasaccharide, the 2- and 4-acetamido- and 2- and 4-lactam analogs of the Lewis x trisaccharide. The key-steps in the syntheses were regio- and stereoselective galactosylations of one common monosaccharide diol acceptor, stereoselective fucosylation and regio- and stereoselective sialylations to yield the oligosaccharidic products in 10-62% over-all yield from monosaccharidic starting materials
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