1,721,065 research outputs found
Sintesi e caratterizzazione di nuovi derivati fullerenici - PRIN 1998
No full textThe chemistry and derivatization of fullerene (C60) continues to attract scientists for the interesting physical properties as well as biological activities. In addition, new materials based on C60 derivatives are promising for their non linear optical behaviour, superconductivity, ferromagnetism and HIV-1 protease inhibition. In these contextes it is possible to justify the interest, in recent years, to the functionalization of C60 and the strong input to this attractive field of research mainly owing to the new prospects that such molecules could offer in the material science area.
One of the goals in C60 chemistry is the preparation of ordered thin films onto various inorganic substrates by Langmuir Blodgett (LB) technique; but, despite few examples of films formation recently reported it is very difficult to produce stable films due to the tendency of such molecules to give auto-aggregation phenomena. For this reason fullerene derivatives opportunely functionalized with hydrophilic pendant groups must satisfy some molecular parameters such as for example a reasonable balance between the hydrophobic and the hydrophilic part in the molecule and the suitable spacer between the hydrophilic pendant and the C60 “sphere”
Optically Active Polyoxotungstates Bearing Chiral Organophosphonate Substituents
No full textDivacant Keggin-type polyoxotungstates [γ-XW10O36]8– with X = Si or Ge, were functionalized with chiral phosphoryl groups. The hybrid compounds [(R*PO)2(γ-XW10O36)]4– with R = N-protected aminoalkyl groups or O-protected amino acid derivatives, were isolated. The solution characterization of the products was performed by different techniques: 183W, 31P, 13C, and 1H NMR spectroscopy, electrospray ionization mass spectrometry, UV/Vis spectroscopy, and circular dichroism (CD). The experimental data confirm the covalent grafting of the organic moieties onto the polyanionic surface. A chirality transfer, from the pendant organic arm to the inorganic framework is apparent from CD studies. Multiple Cotton effects were observed in the region of charge-transfer transitions pertaining to W–O bonds. Furthermore, the 183W NMR spectra are consistent with the expected C2 symmetry, resulting from introduction of two organic stereocenters. The title complexes were used in the presence of hydrogen peroxide to perform the oxidation of methyl p-tolyl sulfide. Implications for the design of enantioselective catalysts based on these derivatives are discussed
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
[Ancient DNA: principles and methodologies.]
No full textPaleogenetics is providing increasing evidence about the biological characteristics of ancient populations. This paper examines the guiding principles and methodologies to the study of ancient DNA with constant references to the state of the art in this fascinating discipli
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
Fast catalytic epoxidation with H2O2 and [gamma-SiW10O36(PhPO)(2)](4) in ionic liquids under microwave irradiation
No full textOlefin epoxidation by [γ-SiW10O36(PhPO)2]4- and H2O2 occurs in hydrophobic ionic liquids (ILs), with yields and selectivity up to >99%. The catalytic IL phase is recyclable. Under MW irradiation the reaction occurs with up to 200 turnovers per minute. Simultaneous cooling is instrumental for quantitative H2O2 conversion
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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