1,721,111 research outputs found
Electrochemistry of Functional Supramolecular Systems
No full textIncorporation of redox-active units in a dendritic architecture enable us to gain information on: (i) dendrimer structure and superstructure; (ii) self-assembly processes; (iii) degree of electronic interaction and communication between redox units located in different sites; (iv) changes in conformation brought about by electron transfer processes. Electroactive dendrimers are attracting increasing interest in view of their possible application as sensors, catalysts, enzyme mimics, in which a redox centre is buried inside the dendritic nanoenvironment, and, last but not least, multielectron storage devices
Molecular Machines and Motors
No full textThe bottom-up construction and operation of machines and motors of molecular size is a topic of great interest in nanoscience and a fascinating challenge of nanotechnology. Research in this field is stimulated by progressive disclosure of the secrets of the natural nanomachines which constitute the material base of life. Examples of artificial nanoscale machines and motors have been built upon various types of molecular and supramolecular species like rotaxanes, catenanes, and DNA. In recent times, the evolution of the structural and functional design of such systems has led to the construction and operation of complex molecular machines that, in some cases, are able to do specific tasks
Electroactive Rotaxanes and Catenanes
No full textThe described systems show the potentialities of electrochemical techniques (the various kinds of voltammetry, chronoamperometry, coulometry, impedance spectroscopy, spectro- and photo-electrochemistry) in characterizing complex systems such as redox-active rotaxanes and catenanes. They provide, indeed, a fingerprint of these systems giving fundamental information on (i) the spatial organization of the redox sites within the molecular and supramolecular structure, (ii) the entity of the interactions between such sites, and (iii) the kinetic and thermodynamic stabilities of the reduced/oxidized and charge-separated species. Electrochemistry is, therefore, a powerful tool to ‘read’ the state of the system.
In suitable designed rotaxanes and catenanes, however, electrochemistry can play a more important role. By causing the occurrence of endoergonic heterogeneous electron-transfer processes electrochemistry can, indeed, provide the energy needed to modify the noncovalent interactions that stabilize a certain rotaxane and catenane structure promoting mechanical movements. In such cases electrochemistry plays the dual role of ‘writing’ and ‘reading’ the system: by means of electrons and/or holes it supplies the energy to make theses systems work as molecular machines, and by means of the various electrochemical techniques it is used for controlling and monitoring the operation performed by the system.
Although the examples described here evidence that electrochemists have learned how to deal with increasingly complex molecular and supramolecular structures, it is important to notice that electrochemistry is only a part of the game: as the complexity of the systems studied increases, the contribution from many disciplines in a joint and collaborative effort is needed. For the intriguing structures here described this statement is particularly true. The goal of transforming molecular devices and machines into practically useful products requires, indeed, that people belonging to different fields, like chemistry, solid-state physics, biology, computer science, mathematics, materials sciences, etc., work together and learn a common language
Dendrimers as Multielectron Storage Devices
Full text linkDendrimers are complex, repeatedly branched tree-like compounds that can be synthesized with well-defined composition and a high degree of order.
Incorporation of redox-active units in a dendritic architecture enable us to gain information on: (i) dendrimer structure and superstructure; (ii) self-assembly processes; (iii) degree of electronic interaction and communication between redox units located in different sites; (iv) changes in conformation brought about by electron transfer processes. Electroactive dendrimers are attracting increasing interest in view of their possible application as sensors, catalysts, enzyme mimics, in which a redox centre is buried inside the dendritic nanoenvironment, and, last but not least, multielectron storage devices
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
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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