1,721,061 research outputs found
The effect of temperature on the photoacidity of merocyanine photoacids in water
Full text linkMerocyanine photoacids are molecular photoswitches that can be used to regulate acid-base reactions reversibly. Despite their growing impact across multiple research areas including materials science and nanotechnology, the effect of temperature on their functioning in aqueous environments has not yet been explored. Here we employ variable-temperature pH and UV-Vis analyses to rationalize their temperature-dependent (photo)chemical behaviors in water, showing that their photoacidity is inversely proportional to the temperature (by ca. −0.01 pK/°C)
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
Photoacidity of Indolinospirobenzopyrans in Water
Full text linkThe reversible isomerism of indolinospirobenzopyrans is perhaps among the most studied phenomena in the field of molecular switches. Although they began to gain attention as early as 70 years ago following the seminal work of Hirshberg and Fischer, who were the first to recognize their photochromic behaviours, their implementation as photoacids emerged prominently only in the last decade. In this Review, we contextualize the prerequisites underlying the photo-triggered proton release that occurs in these molecular switches, highlighting the most recent advances in their characterization and application as "metastable-state photoacids" in water.LC
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
Light-induced assembly and disassembly of polymers with PdnL2n-type network junctions
No full textPolymers containing PdnL2ncomplexes as network junctions were obtained by reaction of poly(ethylene glycol)-linked N-donor ligands with Pd2+. The addition of a metastable state photoacid renders the networks light sensitive, and gel-sol transitions can be achieved by irradiation with light. The inverse process, a light-induced sol-gel transition, was realized by using a molecularly defined Pd complex as an acid-sensitive reservoir for Pd2+. Upon irradiation, Pd2+ions are released, allowing the formation of an acid-resistant polymer network. Both the gel-sol and the sol-gel transitions are reversed in the dark
Wiring proton gradients for energy conversion
No full textLight-switchable buffer solutions based on merocyanine photoacids can be used as efficient photoenergy harvesting systems. Varying the solvation environment of merocyanine photoacids in water-methanol mixtures allows one to carefully tune their photoacidity, relaxation kinetics, and solubility, opening up the possibility to install persistent pH gradients of approximately 4 pH units under 500 nm light. When interfaced between two electrodes and exposed to asymmetric light irradiation, these solutions can be photoactivated precisely both in space and time, generating open circuit voltages as high as 240 mV that can last hours under steady-state irradiation - an outcome that is akin the peak performance of biological transmembrane proton pumps
Conserving imperiled species: a comparison of the IUCN Red List and U.S. Endangered Species Act
No full textAbstract
The United States conserves imperiled species with the Endangered Species Act (ESA). No studies have evaluated the ESA's coverage of species on the International Union for Conservation of Nature (IUCN) Red List, which is an accepted standard for imperiled species classification. We assessed the ESA's coverage of IUCN‐listed birds, mammals, amphibians, gastropods, crustaceans, and insects, and studied the listing histories of three bird species and Pacific salmonids in more detail. We found that 40.3% of IUCN‐listed U.S. birds are not listed by the ESA, and most other groups are underrecognized by >80%. Species with higher IUCN threat levels are more frequently recognized by the ESA. Our avian case studies highlight differences in the objectives, constraints, and listing protocols of the two institutions, and the salmonids example shows an alternative situation where agencies were effective in evaluating and listing multiple (related) species. Vague definitions of
endangered
and
threatened
, an inadequate ESA budget, and the existence of the
warranted but precluded
category likely contribute to the classification gap we observed.
J. Berton C. Harris, J. Leighton Reid, Brett R. Scheffers, Thomas C. Wanger, Navjot S. Sodhi, Damien A. Fordham & Barry W. Broo
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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