1,720,960 research outputs found
Photobehaviour and DNA interaction of styrylquinolinium salts bearing thiophene substituents
No full textA photochemical and photophysical study on three quinolinium iodides, free and complexed with DNA, was carried out by stationary and pulsed techniques. The comparison with the behaviour of pyridinium analogues pointed to a reduction in the photoisomerization yield of these compounds in favour of fluorescence and internal conversion. These quinolinium salts showed a good affinity towards salmon DNA with association constants approximate to 10(4) M(-1) and a different photobehaviour when involved in the formation of ligand-DNA complexes. The drastic reduction of photoisomerization observed under excitation of 1/3-DNA complexes and accompanied by a huge increase of the fluorescence quantum yields was connected to interaction modes favouring intercalation proposed for these planar quinolinium derivatives
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
Photostability of 6-MAM and morphine exposed to controlled UV irradiation in water and methanol solution: HRMS for the characterization of transformation products and comparison with the dry state
No full textThe UVA and UVB light-induced behaviour of 6-monoacetylmorphine (6-MAM) and morphine, the main metabolites of heroin, was studied in methanol, aqueous solution and in the dry state. UVA and UVB irradiations were performed for different times (radiant energies of 20-300 J/cm(2)). UV spectra of irradiated samples were compared with samples kept in the dark. To estimate the extent of photolysis, positive ion electrospray ionization experiments were performed on the irradiated samples by LC-HRMS. Tentative identification of photoproducts was performed on the basis of their elemental formula as calculated by HRMS results. Morphine and 6-MAM demonstrated to be quite stable under UVA light but very sensitive to UVB irradiation. In methanol solutions they undergo a similar pattern, both reaching 90% photodegradation after 100 J/cm(2) of UVB, with a slightly faster kinetic for morphine at lower doses. In water, the yields of photodegradation are nearly one third lower than in methanol. In the solid state, the yield of photodegradation is lower than in solution. The structures of some UVB-induced degradation products are proposed. Photoaddition of the solvent and photooxidation seem the main pathways of phototransformation of these molecules. Moreover, both compounds revealed to generate singlet oxygen under UVB exposure
Studio delle lesioni retiniche in pazienti con poliposi famigliare del colon
No full textStudio delle lesioni retiniche in pazienti con poliposi famigliare del colo
Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push–Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD‐DFT Computational Study
No full textThree (donor–p–acceptor)+ systems with a methyl pyridinium or quinolinium as the electron-deficient group, a dimethyl amino as the electron-donor group, and an ethylene or buta- diene group as the spacer have been investigated in a joint spectroscopic and TD-DFT computational study. A negative sol- vatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by con- sidering the variation in the permanent dipole moment modu- lus and orientation upon photoexcitation. The fluorescence ef-
ficiency decreases upon increasing solvent polarity, in agree- ment with the excited-state optimized geometries (planar in low-polarity media and twisted in high-polarity media). Femto- second transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Consider- ing the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promis- ing NLO materials
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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