1,720,975 research outputs found
Do thermal treatments influence the ultrafast opto-thermal processes of eumelanin?
Full text linkAfter light absorption, melanin converts very rapidly the energy gained into heat. The time scale of this process ranges from tens of femtoseconds to a few nanoseconds. Femtosecond transient absorption allows for exploration of such photo-induced carrier dynamics to observe the de-excitation pathways of the biological complex. Here, we report on the ultrafast relaxation of suspensions of Sepia melanin in DMSO at room temperature using a femtosecond broadband pump and probe technique by photoexciting in the UV and probing in the entire visible range. In particular, we focus on the possible role that different heat treatments, performed in the temperature range 30-80 degrees C might have on the relaxation of charge carriers photogenerated by UV radiation in such suspensions. Experimental data indicate that in all the investigated suspensions, photoexcited carriers always follow a tri-exponential route to relaxation. Moreover, we find that the relaxation time constants are essentially the same in all cases, within the experimental error. We take this as evidence that all the investigated suspensions essentially exhibit the same relaxation dynamics, regardless of the temperature at which the heat treatment has been performed and of the heat-induced denaturation of the proteinaceous compounds bound to the photoactive pigment. Our experiments represent a significant step towards the understanding of the stability of melanin with respect to temperature changes
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
COLLOIDAL TiO2 NANORODS FOR PHOTOCATALYSIS: A FEMTOSECOND TRANSIENT ABSORPTION STUDY
No full textConcept: The excitation-dependent relaxation dynamics of charge carriers in anatase TiO2 nanorods (NRs) was investigated by femtosecond transient absorption spectroscopy. This technique is a widely known effective tool with unique capabilities for elucidating the electron-hole (e--h+) recombination dynamics of nanocrystals. Colloidal dispersions of such anisotropic nanocrystals were excited in the UV−vis range using three different pump wavelengths, i.e. above, close to, and below the direct band gap of anatase. We show that the ultrafast dynamics strongly depends on the excitation wavelength, and influences most of the processes contributing to the relaxation dynamics.
Motivations and objectives: TiO2 nanocrystals are successfully exploited in applications related to energy conversion, such as photocatalysis and photovoltaics, thanks to their ability to generate e--h+ pairs under proper lighting. In addition, the rod-like nanocrystal shape magnifies this effect, due to a larger surface/volume ratio and a higher number of active sites of interaction with the environment. The conversion efficiency is correlated to the lifetimes of e- and h+ before their recombination, which in turn are influenced by several factors. Excitation energy plays a major role, as it defines the initial potential of the carriers. An excitation-dependent investigation of the charge carrier dynamics is thus expected to provide major information crucial for understanding their reactivity and for further rationalizing their behavior in photocatalytic applications.
Results and discussion: TiO2 NRs were synthesized by a colloidal chemistry route and dispersed in an organic solvent, thanks to oleate ions coordinating the nanocrystal surfaces. We performed pump-probe experiments in a weak-excitation regime by pumping at 300, 350, and 430 nm and probing in a broadband spectral range extending from 450 to 750 nm. The temporal evolution of photoinduced absorption changes was found to be strongly dependent on the excitation conditions, both at short and long time delays. Nonetheless, the initial charge carriers trapping in surface defect states occurs very rapidly after the photogeneration in all investigated cases. The two distinct TA bands at 500 and 700 nm, typically attributed to trapped h+ and e- in anatase, are accessible only when TiO2 nanorods are photoexcited well above the band gap, while there is no evidence of such bands when excitation occurs close to or below the band gap. In such cases the observed
dynamics are attributed to excitonic states. This evidence is also supported by the persistence of a long-lasting TA contribution ascribable to such bound states
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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