1,720,958 research outputs found
Light-induced removal of 180° ferroelectric domains in Rh:BaTiO<sub>3</sub>
No full textWe show that optically-induced photorefractive space-charge fields can remove 180° ferroelectric domains in rhodium-doped barium titanate. The cross section of the domains must be small (less than 100 microns) for this process to occur
Amplification of near-infrared light in a photorefractive ring resonator
Full text linkWe have demonstrated efficient amplification of near-infrared, 0.83-0.7µm and 1.06-1.07µm light, in a photorefractive ring resonator using Rh:BaTiO3. The optical power oscillating inside the ring exceeded the pump power by a factor of up to 2.34. The sensitivity of a ring resonator to nanometer changes in its length was characterised using a piezo-mirror
AC Field Enhancement of Diffraction From Permanent Gratings in Dye-Doped Liquid Crystals
No full textPermanent gratings can be written in doped liquid crystals with high dye concentration without any externally applied electric field, using low intensity, visible light. The gratings are adaptive as their diffraction efficiency can be easily modulated and controlled enhanced by an AC field. The diffracted intensity could also be modulated by a low frequency electric field with the magnitude of modulation decreasing for higher frequencies. The permanent gratings are durable, remaining in the cells for over a year even after application of high temperatures
Electric field control of diffraction and noise in dye-doped liquid crystals
No full textWe present results on permanent gratings in highly dye-doped liquid crystal cells without polymer coatings of the cells' surfaces. The surface-mediated gratings remain in cells for months without degradation of their quality. The peak diffraction efficiency can be controlled, enhanced or decreased, by applying low voltage AC field. At low frequencies, below 1 Hz, the diffracted signal can modulated by the AC field, but the time development of the signal shows a complex response. The enhancement of diffraction can be, however, observed at all frequencies we tested (0.1 Hz – 300 kHz). The permanent gratings cannot be removed by heating above the liquid crystal phase transition temperature as on cooling the diffraction efficiency is restored
Near-infrared light amplification in a photorefractive ring resonator
No full textWe have demonstrated efficient amplification of near-infrared, 830nm and 1.06µm light, in a photorefractive ring resonator. The oscillating power exceeded the pump power by up to a factor of 2.35
Optical poling in Rh:BaTiO<sub>3</sub>
No full textWe show that 180° ferroelectric domains can be optically removed from rhodium-doped barium titanate crystals without externally applying an electric field. The experimental technique to remove the domains as well as to detect them are one and the same; it is the method used by Grubsky et al. to detect 180° domains using photorefractive two-beam coupling, known colloquially as the "Swiss cheese technique". We find that if thin domains (less than 100 microns by side) are present, they disappear as the crystal is monitored. In addition, we show that infrared radiation (1.06 nm) can induce the formation of thin 180° domains in well-poled crystals
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
- …
