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Coherent two photon excitation within an extended cloud of Rubidium 85 for the purposes of atomic interferometry and cooling
No full textCold atom samples, at temperatures of the order 100 µK, are useful for a wide reaching array of new and exciting technological and scientific endeavours. Atoms are conventionally cooled by Doppler cooling, which relies on the continuous absorption and re-emission of photons in a closed optical cycle. This requirement is difficult to achieve when there are many allowed decay paths for the excited atom, making Doppler cooling only feasible for a handful atoms with simple energy level structures. More exotic energy level structures, such as those found in molecules, are notoriously difficult to cool. Coherent cooling schemes in comparison, offer advantages such as insensitivity to frequency detuning or a higher number of photon momenta which can be imparted for each spontaneous emission event making them promising candidates for the optical cooling of particles with more general energy level structures. In order to demonstrate these schemes, we have explored the coherent manipulation of an atomic cloud of Rubidium cooled using a two photon Raman resonance. Despite the long spontaneous decay times of such systems, we find a significant decay in the fidelity of the coherent manipulations, which we have characterised using the techniques of Raman spectroscopy, Rabi oscillations, Ramsey interferometry and spin echo. We have found the minimum time constant for the decay in the decoherence to be 2.1fi0:2 ms, which is a result of non-radiative and partially non-stochastic dephasing mechanisms. Due to a high level of decoherence during the spin-echo experiments further investigation is required to determine the exact ratio of stochastic to non-stochastic dephasing
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
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