1,720,963 research outputs found
Sensitivity enhancement of integrated optics sensors by thin high index films
No full textExperimental measurements on waveguide Mach-Zehnder interferometers are presented which show that order of magnitude improvements in the sensitivity of planar waveguide sensors can be achieved by incorporating thin high index overlays
Sensitivity enhancement of integrated optical sensors by use of thin high-index films
No full textThe proportion of power carried in the superstrate medium by the guided modes of integrated optical waveguides can be increased by the addition of a thin high index film. Enhanced refractive index sensing is demonstrated using channel waveguide Mach-Zehnder interferometers with Ta2O5 overlayers. Sensitivity increases by a factor greater than 50, and a detection limit better than 5x10-7 are obtained. This approach is broadly applicable to sensing at waveguide surfaces where the strength of evanescent fields dictates performance
Integrated optical dual Mach-Zehnder interferometer sensor
No full textThe fabrication and operation of robust integrated optical refractometers, suitable for precise measurements of small changes without ambiguity over a wide range of refractive indices, is described. The design primarily uses an optical fibre coupled dual-sensitivity integrated optical Mach-Zehnder Interferometer sensor chip incorporating 3x3 directional coupler combiners and internal referencing. High-index Ta2O5 films were deposited on the waveguide surface in order to increase sensitivity and measurements of their response to liquid analyte index have been carried out by passing aqueous sucrose solutions over the sensor surface. These devices are intended for application as high-sensitivity multi-purpose chemical sensors and biosensors
Immunofluorescence sensor for water analysis
No full textWe demonstrated a bulk optical fluorescence based immunosensor capable for multianalyte water analysis. Calibration curves obtained for 2,4-dichlorophenoxyacetic acid (2,4-D) and simazine had detection limits of 0.035 µg/l and 0.026 µg/1 respectively. The sensor is reusable due to its regenerability and cost effective due to the use of components customary in the trade. Ways to further enhance device sensitivity by means of a high index film deposited on the sensor surface or by employing an integrated optical waveguide as transducer are presented. A concept for the detection of a varying range of analytes on the same transducer is discussed
Ti-diffusion in sapphire for active and passive waveguide devices
No full textFollowing the recent realisation of a Ti:sapphire waveguide laser by Ti-indiffusion, the relation between diffusion conditions, waveguide properties and Ti spectroscopy is discussed in depth with a view to developing a next-generation device
Waveguide immunofluorescence sensor for water pollution analysis
No full textA regenerable channel waveguide fluorescence sensor for environmental monitoring is reported. The sensor has been characterised as a detector of the pesticide 2,4 dichlorophenoxyacetic acid. A binding inhibition assay, using fluorescent Cy5.5 dye-labelled antibodies, was monitored at the modified surface of the glass waveguide to detect the target analyte. Three calibration curves were determined and averaged. The averaged calibration curve has a mid-point of 0.68 ppb and a calculated detection limit of 0.28 ppb. Incorporation of a 20 nm thick tantalum pentoxide film at the waveguide surface enhanced the peak fluorescence signal by a factor of approximately 6 compared with an uncoated sensor. Due to the high optical field strengths at the surface of the waveguide, which is approximately 10µm wide, significant photobleaching of the dye molecules occurs. The rate of photobleaching will be reduced if the power density of the excitation radiation at the surface of the waveguide is reduced, offering the potential for enhanced device sensitivity. This may be achieved, without reducing the total power, by broadening the 10µm wide optical waveguide through a tapered region to a final width in excess of 50µm. A distinct advantage of this broadening is to improve the signal to noise ratio of the sensor as the number of bound fluorophores at the waveguide surface increases linearly with the waveguide width. Theoretical modelling of tapered waveguides, using a beam propagation method package, has indicated that the peak field intensity of radiation in the 10µm guide may be reduced by 85% if the guide is broadened through a taper to a final width of 50µm
Integrated optical immunofluorescence sensor for environmental monitoring
No full textWe have demonstrated a regenerable waveguide fluorescence sensor for environmental monitoring. Characterisation of the sensor as a detector of the pesticide 2,4 dichlorophenoxyacetic acid in water is presented. A binding inhibition assay, using fluorescent Cy5.5 dye-labelled antibodies, was monitored at the modified surface of the glass waveguide to detect the target analyte. Incorporation of a thin high-index film at the waveguide surface enhanced device sensitivity
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
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