1,720,965 research outputs found
The water-like film on water
Full text linkWe have used wavelength scanning close to the Brewster angle of water to determine the relative index of refraction between the surface film and the bulk liquid. The result is clearly that contrary to expectation, the surface film has a higher index than the bulk. This runs counter to molecular dynamics calculations which propose a tapering off of density, and by implication of refractive index. The finding may be more in line with recent suggestions that clusters of hydronium ions may dominate the structure close to the surface
Efficient fluorescence quenching near crystalline silicon from Langmuir–Blodgett dye films
No full textThe distance dependence of the fluorescence efficiency from Langmuir Blodgett (LB) dye layers deposited on top of silicon substrates was studied for different silicon crystal orientations (<100> and <111>). The distance to the silicon surface was varied with stearic acid LB layers (SA). Spectroscopic Ellipsometry (SE) provided accurate measurements of the thickness of the separation steps and the refractive index of the dye layer. It was found that the fluorescence efficiency of the overlying LB dye layers was quenched significantly by the presence of the semiconductor at close distances to the surface. No significant difference in the fluorescence quenching for the LB dye between the two crystal orientations was observed. The results obtained are compared with previous work from fluorescence time and intensity measurements. The importance of interference effects is stressed at high semiconductor-dye distances but the fluorescence quenching observed at small distances is due to efficient energy transfer to the semiconductor
Er:Ta<sub>2</sub>O<sub>5</sub> waveguide optimization & spectroscopy
No full textThe optimization of erbium-doped Ta thin film waveguides deposited by magnetron sputtering is described. Background losses below 0.4dB/cm have been obtained before post-annealing. A broad photoluminescence spectrum centered at 1534nm is obtained, and the photoluminescence power and fluorescence lifetime increase with post-annealing, yielding promising results for compact amplifiers
Comment on “Energy transfer in nanowire solar cells with photon-harvesting shells” [J. Appl. Phys. 105, 124509 (2009)]
No full textIn a recent article, Peters et al. [J. Appl. Phys. 105, 124509 (2009)] claim to have observed photosensitization of crystalline silicon by energy transfer from an optically absorbing thin polymer film.We show that this claim is not justified. Their experimental design is not adequate to establish enhanced photoexcitation of silicon; moreover, the theoretical arguments in their interpretation do not stand up to scrutiny
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
Characterisation of the sea surface microlayer - using Langmuir films and ellipsometry
No full textThe sea-surface microlayer (SSM) is a hugely complex system comprised of many different organic materials that has a considerable influence on the physical and chemical properties of the ocean surface. Under certain conditions, involving wind, internal waves and currents, the SSM is compressed and forms biogenic slicks. These biogenic slicks have a wave dampening effect and when using satellite data to monitor the ocean surfaces look indistinguishable from anthropogenic slicks. It is important to understand the physical properties of these biogenic slicks to identify oil pollution.
For this project the physical properties of biogenic slicks from the Solent (UK) and the Black Sea (Ukraine) are being investigated. Model compounds that display similar properties to the slicks are also being characterized; these simpler systems are easier to interpret and parallels to the biogenic slicks can be made increasing understanding.
The tools used to characterize these Langmuir films involve the analysis of the phase and amplitude change of polarized light upon surface reflection (ellipsometry). The film can be compressed and expanded monitoring changes in surface pressure. In conjunction, ellipsometry can be used to determine optical properties, thickness, phase changes and hysteresis effects of the film, offering both spectroscopic information and images. The changes of the film on compression are important as they mimic natural events that have the potential to be of use in satellite data interpretation.
Results show, in images, the domain separation of different chemical species within the SSM and co-existence of phases. Upon compression and expansion of the films, aggregation of the different phases along with hysteresis effects are seen – phenomena that has only been hypothesized so far. Work on the model compounds demonstrates that it is possible to determine thicknesses of thin films at different surface pressures offering valuable information on phase changes
Second harmonic ellipsometry
No full textApparatus suitable for variable wavelength and incident angle second harmonic ellipsometry (SHE) studies of solid and liquid interfaces is introduced, with particular attention drawn to the calibration of the experiment. Preliminary results obtained from the study of the chiral molecule 1, 1'-bi-2-naphthol located at the air/water interface are used to indicate the suitability of SHE as a surface probe for resonant systems including the determination of the interfacial refractive index at the harmonic frequency
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