1,721,005 research outputs found
Experimental investigation of ultrafast internal conversion in aniline and 1,4-diazabicyclo[2.2.2]octane (DABCO)
Full text linkPump-probe time-resolved photoelectron spectroscopy is employed to investigate ultrafast non-adiabatic dynamics in aniline, deuterated aniline (aniline-D7) and 1,4- diazabicyclo[2.2.2]octane (DABCO). Aniline molecules are photoexcited over a wide range of wavelengths between 269 and 236 nm. Our observations reveal direct population of the S2(π3s/πσ∗) state. The photoelectron energy and angular distributions obtained in our experiments show an interesting bifurcation of the Rydberg population to two non-radiative decay channels. One of these involves ultrafast relaxation from the Rydberg component of the S2(π3s/πσ∗) state to the S1(ππ∗) state, from which the population relaxes back to the electronic ground state on a much longer timescale. The other channel appears to involve motion along the πσ∗dissociative potential energy surface. At higher excitation energies, the dominant excitation is to the S3(ππ∗) state, which undergoes extremely efficient electronic relaxation back to the ground state. Aniline-D7 is photoexcited with 260 nm wavelength light. The photodynamics of aniline-D7 is similar to those observed in aniline. Comparison of the dynamics of aniline and aniline-D7confirm that the relaxation of the π3s component of the S2(π3s/πσ∗) state to the S1(ππ∗) state is a main relaxation pathway. Photodynamics of DABCO molecules were also studied over a wide range of wavelengths between 251 and 234 nm. The ultrafast internal conversion in DABCO between the S2 3px,y(+) and S1 3s(+) Rydberg states follows a biexponential decay. It was found that initial randomly oriented molecules are partially aligned after absorption of linearly polarised light and, therefore, DABCO exhibits a preferential direction of excitation
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
The role of πσ* states in the ultrafast non-radiative dynamics of pyrrole, aniline and phenol
No full textThis thesis comprises three time-resolved photoelectron imaging (TRPEI) studies, examining the ultraviolet (UV) photorelaxation dynamics of molecules with low-lying πσ* states. Chapter 1 introduces important principles in molecular photochemistry, wavepacket dynamics and the relaxation mechanisms enabled by these πσ* states. Chapter 2 describes the experimental apparatus and data analysis techniques used to extract information from raw TRPEI spectra. Chapters 3-5 contain the experimental data. Chapter 3 examines the UV relaxation dynamics of pyrrole, where the lowest excited singlet state is of πσ* character. We observe a single sub-50 fs, dissociative decay for all wavelengths studied, in keeping with the literature. The pyrrole dimer is used as a model for microsolvation, where a new decay pathway opens, relating to relaxation into stabilised charge transfer states. Chapter 4 details the experimental study of aniline. Direct excitation to the S2 with various excess vibrational energies, shows that the S2/S1 conical intersection is located close to the S2(πσ*) origin and enables the dominant S2 → S1 internal conversion mechanism. Population on the S1(ππ*) surface (following relaxation or direct excitation) undergoes considerably slower internal conversion to the ground state, the invariance of this decay in deuterated aniline suggests that any S1 → S2 tunnelling is not favoured. Chapter 5 studies the UV photodynamics of phenol, finding that internal conversion to the ground state is the dominant relaxation mechanism in the S1(ππ*) state, in agreement with the literature. Increasing the excitation energy to access to the S2(πσ*) state opens a minority pathway to O-H dissociation, but IVR on the S1 surface followed by internal conversion continues to dominate. Finally, Chapter 6 summarises the surprising variety in the mechanisms that πσ* states facilitate, even in these closely related molecules, and provides an outlook for future work
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
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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