Filters
Availability
Publication Year
Resource Type
Faculty
School/Institute
Publication Search Results
Sort
Results per page
1 - 10 of 76
-
(1996)Journal ArticleThin film crystalline silicon solar cells can only achieve high efficiencies if light-trapping can be used to give a long optical path lengtrh, while simulatneously achieving near unity collection probabilities for all generated carriers. This necessitates a supporting substrate of a foreign material, with refractive index compatible with light trapping schemes for silicon. The resulting inability to nucleate growth of crystalline silicon films of good crystallographic quality on such foreign substrates, at present prevents the achievement of high efficiecny devices using conventional single junction solar cell structures. The parallel multijunction solar cell preovides a new approach for achieving high efficiencies from very poor quality material, with near unity collection probabilities for all generated carriers achieved through appropriae junction spacing. Heavy doping is used to minimise the dark saturation current contribution from the layers, therefore allowing respectable voltages. The design strategy, corresponding advantages, theoretical predictions and experimental results are presented.
-
(1996)Journal ArticleThis paper provides a theoretical investigation of recombination at grain boundaries in both bulk and p-n junction regions of silicon solar cells. Previous models of grain boundaries and grain boundary properties are reviewed. A two dimensional numerical model of grain boundary recombination is presented in this paper. This numerical model is compared to existing analytical models of grain boundary recombination within both bulk and p-n junction regions of silicon solar cells. This analysis shows that, under some conditions, existing models poorly predict the recombination current at grain boundaries. Within bulk regions of a device, the effective surface recombination velocity at grain boundaries is overestimated in cases where the region around the grain boundary is not fully depleted of majority carriers. For vertical grain boundaries (columnar grains), existing models are shown to underestimate the recombination current within p-n junction depletion regions. This current has an ideality factor of about 1.8. An improved analytical model for grain boundary recombination within the p-n junction depletion region is presented. This model considers the effect of the grain boundary charge on the electric field within the p-n junction depletion region. The grain boundary charge reduces the p-n junction electric field, at the grain boundary, enhancing recombination in this region. This model is in agreement with the numerical results over a wide range of grain boundary recombination rates. In extreme cases, however, the region of enhanced, high ideality factor recombination can extend well outside the p-n junction depletion region. This leads to a breakdown of analytical models for both bulk and p-n junction recombination, necessitating the use of the numerical model.
-
(1997)Journal ArticleAcoustic resonances of the vocal tract give rise to formants (broad bands of acoustic power) in the speech signal when the vocal tract is excited by a periodic signal from the vocal folds. This paper reports a novel instrument which uses a real-time, non-invasive technique to measure these resonances accurately during phonation. A broadband acoustic current source is located just outside the mouth of the subject and the resulting acoustic pressure is measured near the lips. The contribution of the speech signal in the pressure spectrum is then digitally suppressed and the resonances are calculated from the input impedance of the vocal tract as a function of frequency. The external excitation signal has a much smaller harmonic spacing than the periodic signal from the vocal folds and consequently the resonances are determined much more accurately due to the closer sampling. This is particularly important for higher pitched voices and we demonstrate that this technique can be markedly superior to the curve-fitting technique of linear prediction. The superior frequency resolution of this instrument which results from external vocal tract excitation can provide the precise, stable, effective, articulatory feedback considered essential for some language-learning and speech therapy applications.
-
(1997)Journal ArticleThe magnetization of melt-textured Y-123 and single crystal La-214 has been measured in magnetic field up to 5.5 T using a SQUID magnetometer. Partial and nearly complete flux jumps were observed at about 10 K in Y-123 and 5 K in La-214 single crystals, respectively.
-
(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.
-
(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.
-
(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.
-
(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.
-
(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.
-
(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.