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Van der Waals explosion of cold Rydberg clusters
Get PDFWe report on the direct measurement in real space of the effect of the van der Waals forces between individual Rydberg atoms on their external degrees of freedom. Clusters of Rydberg atoms with interparticle distances of around 5μm are created by first generating a small number of seed excitations in a magneto-optical trap, followed by off-resonant excitation that leads to a chain of facilitated excitation events. After a variable expansion time the Rydberg atoms are field ionized, and from the arrival time distributions the size of the Rydberg cluster after expansion is calculated. Our experimental results agree well with a numerical simulation of the van der Waals explosion
Dissipative and non-dissipative many-body dynamics in a cold Rydberg gas
No full textDissipative and non-dissipative many-body dynamics in a cold Rydberg ga
Strongly correlated excitation dynamics in an ultracold Rydberg gas
No full textThe van-der-Waals interaction between ultracold atoms excited to highlying Rydberg states can lead to strongly correlated excitation dynamics [1, 2]. We study these correlations for resonant and off-resonant driving of cold atoms in a magneto-optical trap. In the resonant case we observe dynamical constraints similar to those found in glassy systems [3]. By contrast, for off-resonant driving facilitated excitations mediated by Rydberg-Rydberg interactions lead to avalanche-like events in which a chain reaction of successive excitations occurs. We show that this effect can be induced by a seed excitation and that the resulting full counting statistics of excitation events can be reproduced by a simple analytical model
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Optical Gain Switching by Thermo‐Responsive Light‐Emitting Nanofibers through Moisture Sorption Swelling
No full textThe development of intelligent photonic systems made of stimuli-responsive materials, i.e., with features tunable and switchable by environmental signals, is gaining increasing attention. Here, the study reports on switchable optical gain based on complex arrays of nanofibers made of thermo-responsive poly(2-n-propyl-2-oxazoline), incorporating a blue-emitting chromophore. The fluorescent component endows the nanofibers with optical gain in addition to the moisture absorption capability of the polymer. Light amplification is found with temperature- and humidity-dependent excitation threshold. The threshold value is halved close to the polymer cloud point temperature, enabling reversible switching of the emission intensity upon temperature change. Waveguiding analysis by back-focal plane imaging on individual fibers allows the switching mechanisms to be rationalized, in terms of moisture sorption swelling-induced morphological changes. These responsive light-emitting nanofibers may find application in a novel class of lasers with dynamically-controlled properties, environmentally-switchable optoelectronics, and smart sensors
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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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