InGaAsP annular Bragg lasers: theory, applications, and modal properties

A novel class of circular resonators, based on a radial defect surrounded by Bragg reflectors, is studied in detail. Simple rules for the design and analysis of such structures are derived using a transfer matrix formalism. Unlike conventional ring resonators, annular Bragg resonators (ABR) are not limited by the total internal reflection condition and can exhibit both large free spectral ranges and low bend losses. The Bragg reflection mechanism enables the confinement of light within a defect consisting of a low refractive index medium (such as air). Strong atom-photon interaction can be achieved in such a structure, making it a promising candidate for sensing and cavity quantum electrodynamics applications. For sensing applications, we show that the ABR structure can possess significantly higher sensitivity when compared to a conventional ring resonator sensor. Lasing action and low threshold levels are demonstrated in ABR lasers at telecommunication wavelengths under pulsed optical pumping at room temperatures. The impact of the intensity and dimensions of the pump spot on the emitted spectrum is studied in detail.     

CASSM and cognitive walkthrough: usability issues with ticket vending machines

We focus on the ability of two analytical usability evaluation methods (UEMs), namely CASSM (Concept-based Analysis for Surface and Structural Misfits) and Cognitive Walkthrough, to identify usability issues underlying the use made of two London Underground ticket vending machines. By setting both sets of issues against the observed interactions with the machines, we assess the similarities and differences between the issues depicted by the two methods. In so doing we de-emphasise the mainly quantitative approach which is typical of the comparative UEM literature. However, by accounting for the likely consequences of the issues in behavioural terms, we reduced the proportion of issues which were anticipated but not observed (the false positives), compared with that achieved by other UEM studies. We assess these results in terms of the limitations of problem count as a measure of UEM effectiveness. We also discuss the likely trade-offs between field studies and laboratory testing.     

Development of an ultrasonic system for submarine hull acoustic cladding inspection

A computer controlled ultrasonic measurement and data analysis system has been developed to establish the bonding characteristics of polymer based tiles used on the external hulls of UK submarines to reduce sonar reflection and radiated noise. This paper describes the evolvement of the system from laboratory to field site and discusses the selection of hardware components, system integration and the development of the specialized software necessary to initiate and monitor the scanning procedure. The system has been developed to have the versatility to survey either individual or a number of adjacent tiles. Measurement of disbond characteristics is accomplished by the use of C-scan techniques supported by B-scan data and other software processes. Absolute and percentage disbond areas can be calculated to allow acceptance criteria to be applied. The system can also be used as a training and QA tool. Trials on a submarine in refit have demonstrated the efficacy of the technique and early results are given.     

The effectiveness of aluminizing in protecting iron-base alloys in sulphidizing gases at high temperature

Following earlier research which has shown that Al₂O₃ scales are more effective than Cr₂O₃ scales in protecting iron-nickel-base alloys against sulphur-containing gases, several commercial steels, 310 stainless, 314 stainless, and 321 stainless, and an experimental ferritic steel, FeCrAlHf, have been pack aluminized to develop aluminide coatings for applications in mixed-gas environments of high sulphur and low oxygen potential. Results are presented for long-term exposures to H₂/1.6% H₂O/1.1% H₂S at H₂S at 750°C and 1000°C under thermal-cycling conditions. Short-term tests in this environment at 750° C led to considerable sulphidation of the uncoated, Cr₂O₃-forming alloys. The aluminized alloys were much more resistant to sulphidation than the uncoated materials, with relatively little degradation being observed after 200 hr at 750°C. Even at 1000°C, with the exception of the ferritic steel, the coated systems showed reasonable degradation resistance for 500 hr. Eventual sulphidation resulted from back diffusion of aluminum into the substrate and dilution of the coating surface in this element until an Al₂O₃ scale was unable to reform and base metal sulphides could develop. The composition of the substrate was important in determining the rate of aluminium depletion from the coating, with interdiffusion being faster in ferrite-rich matrices than the austenite matrices. Thus, the higher nickel-containing alloys developed the most effective coating systems for use in such environments. The structures of the various aluminized systems are presented and their mechanisms of protection and breakdown are discussed and correlated with their performances under these high-temperature conditions.     

Detection of discoloration in thermally processed blue crab meat

This study objectively and quantifiably examined the effect of a series of factors on blue crab meat discoloration. Factors explored include heating process, animal harvest location, and position of meat within a container. A Spectrogard colorimeter was used to collect visual reflectance spectra between 380 and 720 nm. Meat degree of coloration was characterised objectively and rapidly by using lightness (L), red–green (a) and yellow–blue (b) colour values. Results showed that meat became darker with increasing heating process; crab harvest location had significant effect on the lightness of the flesh; and meat that is located in the bottom of a can was darker than that in the top. This study will serve as a baseline for the development of a coloration quality control system. © 1999 Society of Chemical Industry     

Event Report. Brain Sport: The 1996 World Solar Challenge Solar Car Race Across Australia

In November 1996, a field of 46 solar cars left Darwin bound for Adelaide, some 3000 km to the south. The first car to complete the course, the Honda Dream, set a new race record, maintaining an average speed of 89.9 km per hour (56 mph) over the 4 days. This report describes the highlights of the race and discusses the solar cell and array technology used by the leading cars. © 1997 John Wiley & Sons, Ltd.     

High-efficiency Multicrystalline Silicon Solar Cells using Standard High-temperature,Float-zoned Cell Processing

This paper reports recent results of fabricating multicrystalline silicon solar cells with the standard PERL (passivated emitter, rear locally-diffused) cell high-temperature processing sequence originally developed for float-zoned wafers. One of these multicrystalline silicon cells with a planar front surface demonstrated a 645-mV open-circuit voltage and 18.2% energy conversion efficiency tested at the National Renewable Energy Laboratory and Sandia National Laboratories under the 100 mW cm⁻² AM1.5 global spectrum at 25°C. This is the highest confirmed voltage and one of the highest confirmed conversion efficiencies ever reported to date for a multicrystalline silicon cell. Further optimization of the standard PERL processing and texturing of the cell surfaces is expected to improve the cell efficiency to over 19% in the near future. © 1997 John Wiley & Sons, Ltd.     

Solar cell efficiency tables (version 12)

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since January 1998 are briefly described. © 1998 John Wiley & Sons, Ltd.     

Silicon solar cells

The key attributes for achieving high-efficiency crystalline silicon solar cells are identified and historical developments leading to their realization discussed. Despite the achievement of laboratory cells with performance approaching the theoretical limit, commercial cell designs need to evolve significantly to realize their potential. In particular, the development of cell structures and processes that facilitate entirely activated device volumes in conjunction with well-passivated metal contacts a nd front and rear surfaces is essential (and yet not overly challenging) to achieve commercial devices of 20% efficiency from solar-grade substrates. The inevitable trend towards thinner substrates will force manufacturers to evolve their designs in this direction or else suffer substantial performance loss. Eventually, a thin-film technology will likely dominate, with thin-film crystalline silicon cells being a serious candidate. Present commercial techniques and processes are in general unsuitable for t hin-film fabrication, with even greater importance placed on the achievement of devices with entirely activated volumes (diffusion lengths much greater than device thicknesses), well-passivated metal contacts and surfaces and the important inclusion of li ght trapping. The recent achievement of 21.5% efficiency on a thin crystalline silicon cell (less than 50 μm thick) adds credibility to the pursuit of crystalline silicon in thin films, with a key attribute of this laboratory cell being its extremely good light trapping that nullifies the long-term criticism of crystalline silicon regarding its poor absorption properties and correspondingly perceived inability to achieve high-performance thin-film devices. For low-cost, low-quality polycrystalline sil icon material, the parallel-multijunction cell structure may provide a mechanism for achieving entirely activated cell volumes with the potential to achieve reasonable efficiencies at low cost over the next decade.     

On inner-outer factorization

The calculation of an inner-outer factorization of a proper, rational matrix by state-space methods is considered. Particular attention is given to the extraction of the inner factor, so that a minimal realization is obtained for this factor.