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(2007)Journal ArticleDrying shrinkage and creep are two of the most important time-dependent properties of concrete, and the health monitoring of any large-scale concrete structure is practically the monitoring of the combined effects of these two physical properties. We present a fibre-optic sensing technique using fibre Bragg grating (FBG) sensors for the experimental investigation of drying shrinkage and creep of structural grade (40 MPa) concrete. It offers many advantages over the conventional electrical and mechanical methods for both structural health monitoring and standard tests of the mechanical properties. The FBG sensors are directly embedded into concrete specimens and the data are obtained by an optical measurement system. Standard mechanical method, as specified by the Australian Standards, is also used for comparison. Good agreements between the two methods are achieved for both drying shrinkage and creep. The long-term behaviours are predicted from the experimental data, and the accuracies of prediction are discussed. This optical technique can yield a strain resolution of better than 3 ìå.
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(2001)Journal ArticleThe enhanced backscattering from organic laser gain media that are bounded with one-dimensional (1-D) and two-dimensional (2-D) rough metal films was investigated. We prepared several organic optical gain materials by doping laser-active dyes in matrices of acrylic polymers. These materials produced efficient and broadband fluorescence emission in the visible wavelengths during the pumping of a pulsed YAG or cw argon laser. These gain materials were sliced and coupled with 1-D or 2-D randomly rough gold films with large slopes. An experimental investigation was carried out with a He–Ne laser as the scattering source and the optical gain provided by a cw argon laser. The enhanced backscattering and the satellite peaks located about the enhanced-backscattering peak were obviously amplified, with their widths narrowed. These experimental results agree well with previous theoretical predictions.
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(2007)Journal ArticleThe physical properties of reactive powder concrete (RPC) at early-age, i.e., the first 24 h from casting, and up to an age of 7 days is investigated experimentally using fibre Bragg gratings (FBGs), a type of fibre-optic sensors. A number of FBG sensors are multiplexed together and embedded directly into the RPC specimens, and the shrinkage and temperature change are measured directly and simultaneously. The final setting time and specimen size effect were also investigated. Results showed that there is an interplay between the shrinkage and temperature. The overall shrinkage for 7 days is 488 ìå, with the early-age shrinkage contributing about 77% of this. The temperature curve exhibits a double peak behaviour, with the first peak appears at about 7 h, which is the final setting time. There is a size effect in that smaller prisms have a higher overall shrinkage and lower temperature change than larger prisms. © 2007 Elsevier Ltd. All rights reserved.
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(2007)Journal ArticleFibre Bragg Grating (FBG) sensors were embedded into cement mortar and ultra-high strength reactive powder concrete (RPC) prisms. Thermal tests are performed to accurately characterise the coefficient of thermal expansion (CTE) of these prisms using the measured signals from the embedded sensors. With the use of the fibre optic sensors, the difficulties inherent in using conventional techniques, such as strain gauges or vibrating wire gauges, to measure the thermal properties of cementitious materials are overcome. The error values associated with the measurements, typically measured to be as low as ± 0.04 ìå/K, are a full order of magnitude less than what is expected for standard conventional testing using a length comparator. © 2007 Elsevier Ltd. All rights reserved.
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(2009)Journal ArticleRecently, subband frame-averaged frequency modulation (FM) as a complementary feature to amplitude-based features for several speech based classification problems including speaker recognition has shown promise. One problem with using FM extraction in practical implementations is computational complexity. Proposed is a computationally efficient method to estimate the frame-averaged FM component in a novel manner, using zero crossing counts and the zero crossing counts of the differentiated signal. FM components, extracted from subband speech signals using the proposed method, form a feature vector. Speaker recognition experiments conducted on the NIST 2008 telephone database show that the proposed method successfully augments mel frequency cepstrum coefficients (MFCCs) to improve performance, obtaining 17% relative reductions in equal error rates when compared with an MFCC-based system.
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(2008)Journal ArticleGoal: To identify any major factors that could affect patients` perceptions of a Home Telecare Management System (HTMS) and use the findings to contribute to development of a theoretical framework for patient acceptance of HTMS. Materials and methods: Ten Focus Group Interviews (FGIs) were conducted with patients suffering from congestive heart failure (CHF), chronic obstructive pulmonary disease (COPD), or both, from seven different ethnic groups in Sydney. Six key discussion points were used to conduct the FGIs. The participants were shown a video demonstrating the HTMS and its operation, followed by the demonstration of an HTMS prototype. The participants, who had no prior experience with the HTMS, were then asked questions to access their perceptions in potentially real situations. The discussions were audio-taped and content analysis performed. Results: Four major themes and 16 sub-themes were identified.
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(2006)Journal ArticleTwo kinds of special long period fiber gratings, phase shift and apodised long period gratings, were studied by many researchers, because of their special spectral charateristics. According to the thoery of long-period moir e gratings, with the methods of step-by-step ultraviolet (UV) writing and double exposure with different grating period, several kinds of long-period moir e gratings were fabricated in the hydrogened high germanium doped fiber by controlling the period, several kinds of long period moir egratings were fabricated in the hydrogened high germanium doped fiber by controlling the period and the first position of both exposure and the exposure time of each step, which realized the effects of phase shift and apodization.
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(2006)Journal ArticleEight carrier modulated gratings having the same Bragg wavelength but different carrier frequencies were multiplexed together. The gratings were interrogated and the resultant measurements were processed in such a way to separate out the measurand induced changes of each of the differing carrier components corresponding to each sensor grating. The worst-case scenario for measurement error and crosstalk is investigated.
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(2001)Journal ArticlePhotosensitivity in a perfluoropolymer (CYTOP) optical fibre is investigated. Significant diffraction has been observed from transmission gratings made from the fibre. A maximum diffraction efficiency of 1.6% has been achieved, corresponding to an index change ~= 3 × 10-4. This study demonstrates for the first time the existence of significant photosensitivity and the feasibility of writing Bragg grating in CYTOP fibres.
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(2007)Journal ArticleThe composite cavity fibre laser (CCFL) based on doped fibre and fibre Bragg gratings is described. Due to the fully fibre integrated nature, a CCFL presents distinctive features from semiconductor based multiple cavity lasers, or self injected lasers with external cavity. In particular, the CCFL's internal active feedback property is discussed, and it's ability to sustain single longitudinal mode operation.
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