1,720,957 research outputs found
Tuning localized plasmons in nanostructured substrates for surface-enhanced Raman scattering
No full textComprehensive reflectivity mapping of the angular dispersion of nanostructured arrays comprising of inverted pyramidal pits is demonstrated. By comparing equivalently structured dielectric and metallic arrays, diffraction and plasmonic features are readily distinguished. While the diffraction features match expected theory, localised plasmons are also observed with severely flattened energy dispersions. Using pit arrays with identical pitch, but graded pit dimensions, energy scaling of the localised plasmon is observed. These localised plasmons are found to match a simple model which confines surface plasmons onto the pit sidewalls thus allowing an intuitive picture of the plasmons to be developed. This model agrees well with a 2D finite-difference time-domain simulation which shows the same dependence on pit dimensions. We believe these tuneable plasmons are responsible for the surface-enhancement of the Raman scattering (SERS) of an attached layer of benzenethiol molecules. Such SERS substrates have a wide range of applications both in security, chemical identification, environmental monitoring and healthcare
Determination of nonlinear refractive index in a Ta2O5 rib waveguide using self-phase modulation
No full textSelf-phase modulation has been observed for ultrashort pulses of wavelength 800nm propagating through a 1 cm-long Ta2O5 rib waveguide. The associated nonlinear refractive index n2 was estimated to be 7.23×10-19 m2/W, which is higher than silica glass by more than one order of magnitude. Femtosecond time of flight measurements based on a Kerr shutter configuration show that the group velocity dispersion is small at a wavelength of 800 nm, confirming that dispersion may be neglected in the estimation of n2 so that a simplified theory can be used with good accuracy
Fabrication and optimization of Tantalum Pentoxide waveguides for optical micro-propulsion
No full textDesign, fabrication and optimization of high refractive index (2.1 @ 1070 nm), sub-micron thickness (200 nm) Tantalum Pentoxide waveguides is reported. Optimization of fabrication parameters reduces the propagation loss to ~ 1 dB/cm @ 1070 nm for Ta2O5 waveguides. Ta2O5 waveguides were found to be stable for high power application with no significant absorption peaks over a large range of wavelengths (600-1700 nm). Ta2O5 waveguides provide high intensity in the evanescent field, which is useful for efficient optical propelling of micro-particles. We have employed Ta2O5 waveguide to propel polystyrene micro-particles with 50 µm/s velocity
Experimental and theoretical investigation of loss issues in photonic crystal slab waveguide devices
No full textIn this paper we demonstrate ultra-low loss transmission across a photonic crystal super-prism device consisting of 600 lattice periods etched into a slab waveguide at wavelengths both above and below the primary band-gap. By modifying the refractive index of the holes we have reduced overall insertion loss to 4.5 dB across the entire visible region of the spectrum, greatly enhancing transmission and extinction in higher order stop-bands. In addition we show that the remaining loss is predominantly due to impedance mismatch at the boundary between patterned / unpatterned slab waveguide regions and so is no longer proportional to the length of the photonic crystal or the number of lattice periods. This is an important step forward for the realization of functional photonic crystal time delay elements, dispersion compensators and super-prism spectrometer devices. Experimental loss measurements compare extremely well with Finite difference time domain simulations which were used to investigate the effect of etch depth on scattering loss. We find that partial penetration into the underlying buffer region causes massive scattering loss to substrate modes due to loss of waveguiding in the holes
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
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
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