1,720,961 research outputs found
Design of a compliant-cylinder-type fiberoptic accelerometer - theory and experiment
No full textExperimental and theoretical research was carried out in order to establish the dependence of the performance of a compliant-cylinder-based fiber-optic accelerometer on the geometry and elastic properties of the transducer cylinders. The sensitivity and the natural frequency of the sensor were measured as a function of the ratio epsilon = (inner cylinder diameter)/(outer cylinder diameter). Two transducer materials with different elastic properties, a silicone rubber (Ecosil) and a polyetheretherketone polymer (PEEK 450G), were examined. It was found that with decreasing epsilon the sensitivity increases in the case of Ecosil. and decreases in the case of PEEK. In both cases the natural frequency increases with decreasing epsilon. A simple analytical model was developed in order to explain this behavior qualitatively. The model takes into account the contributions to the effective stiffness from both the cylinder material and the fiber wrapped around the cylinder. The model is useful for the design of such types of accelerometer
Selective coupling of fibre modes using surface-guided Bloch modes supported by dielectric multilayer stacks
No full textThe surface-guided Bloch modes guided by the interface between a multilayer dielectric stack and an external medium are highly dispersive. This makes attractive their use in mode-selective coupling of light into and out of side-polished multimode fibres. The particular case of a dual-mode fibre is modelled in this paper. Mode selection via surface-guided Bloch modes is found to offer advantages in comparison to selection via a single mode waveguiding film of the same average refractive index as the stack. Good modal selectivity is achievable together with high tunability, i.e., high sensitivity to the refractive index of the intervening layer between stack and side-polished fibre
Dispersion, tunability and applications of defect modes in photonic band-gap structures
No full textElectronic surface states, whose energies lie within the semiconductor band-gap, are normally regarded as a nuisance to be avoided in semiconductor lasers. This is particularly true of micro-pillar laser arrays where the surface-area-to-volume ratio is large. Similarly, intra-photonic-band-gap interface or surface states will reduce the effectiveness of a photonic bandgap material by introducing intra-band-gap states into which unwanted spontaneous emission and lasing can occur. These are not, however, always undesirable. Examples include: i) the DFB laser mode supported by a structural defect at the centre of a uniform Bragg mirror - the resonant frequency of this mode lies within the photonic bandgap of the Bragg mirror; ii) the surface-guided Bloch modes (SGBM) confined at the surface of multilayer stacks; and iii) Bragg waveguide modes (BWGM) in which total internal reflection is replaced by Bragg reflection between two multilayer stacks. A general feature of defect modes is a phase velocity that is highly sensitive both to optical frequency and to the "strength" of the local aperiodicity that defines the defect. Small compositional and structural changes can radically alter the position of the mode within the stop-band, providing an effective tuning mechanism. Owing to these and other unique properties, defect modes may provide the basis for the development of a versatile new family of optoelectronic devices. In this paper we discuss some properties of SGBM's within the context of photonic bandgaps and show how they can be used to realize a tunable narrow-band fibre tap and a mode-selective fibre coupler
Transducer mechanism of an optical fiber accelerometer based on a compliant cylinder design
No full textThe dependence of the performance of a compliant cylinder accelerometer upon the geometrical depths and elastic properties of the transducer cylinders is examined experimentally. A simple analytical model was developed in order to explain the experimental results qualitatively
Narrow-band waveguide taps using photonic surface modes supported by multilayer dielectric stacks
Get PDFThe photonic surface modes supported by multilayer dielectric stacks are highly dispersive. They can therefore be used to design mode-selective taps and narrow-band notch transmission filters for waveguide applications
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
