Development of Integrated Thermionic Circuits for High-Temperature Applications

This paper describes a class of microminiature, thin-film devices known as integrated thermionic circuits (ITC) capable of extended operation in ambient temperatures up to 500°C. The evolution of the ITC concept is discussed. A set of practical design and performance equations is demonstrated. Recent experimental results are discussed in which both devices and simple circuits have successfully operated in 500°C environments for extended periods of time (greater than 11000 h).     

Very compact external cavity diffraction-coupled tapered laser diodes

To maintain the same beam quality as that of a single emitter and to be close to diffraction limit, we have combined a phase corrected array, emitting at lambda = 975 nm, coherently using the Talbot effect. First, to improve the beam quality of the array, a phase correcting system was added. The FWHM divergences of the array (which is approximately the same as that of the single emitter since the emitters within the array are not optically coupled to each other) were reduced from 34 degrees to 0.17 degrees in the fast axis and from 3.5 degrees to 0.7 degrees in the slow axis at 6 A. Then, to be close to the diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained a quasi-monolobe slow axis far field profile for the in-phase mode with a central peak divergence of only 0.27 degrees at 1.5 A, 315 mW under cw operation, and of only 0.20 degrees at 2.5 A, 787 mW under pulsed operation. To our knowledge, this is the first demonstration of coherent coupling of a corrected tapered laser diode array in an external Talbot cavity.     

Structure, cell wall elasticity and polysaccharide properties of living yeast cells, as probed by AFM

Although the chemical composition of yeast cell walls is known, the organization, assembly, and interactions of the various macromolecules remain poorly understood. Here, we used in situ atomic force microscopy (AFM) in three different modes to probe the ultrastructure, cell wall elasticity and polymer properties of two brewing yeast strains, i.e. Saccharomyces carlsbergensis and S. cerevisiae. Topographic images of the two strains revealed smooth and homogeneous cell surfaces, and the presence of circular bud scars on dividing cells. Nanomechanical measurements demonstrated that the cell wall elasticity of S. carlsbergensis is homogeneous. By contrast, the bud scar of S. cerevisiae was found to be stiffer than the cell wall, presumably due to the accumulation of chitin. Notably, single molecule force spectroscopy with lectin-modified tips revealed major differences in polysaccharide properties of the two strains. Polysaccharides were clearly more extended on S. cerevisiae, suggesting that not only oligosaccharides, but also polypeptide chains of the mannoproteins were stretched. Consistent with earlier cell surface analyses, these findings may explain the very different aggregation properties of the two organisms. This study demonstrates the power of using multiple complementary AFM modalities for probing the organization and interactions of the various macromolecules of microbial cell walls.     

Life-cycle assessment of greenhouse gas emissions from dairy production in Eastern Canada: A case study

The objective of this study was to conduct a life-cycle assessment (LCA) of greenhouse gas (GHG) emissions from a typical nongrazing dairy production system in Eastern Canada. Additionally, as dairying generates both milk and meat, this study assessed several methods of allocating emissions between these coproducts. An LCA was carried out for a simulated farm based on a typical nongrazing dairy production system in Quebec. The LCA was conducted over 6 yr, the typical lifespan of dairy cows in this province. The assessment considered 65 female Holstein calves, of which 60heifers survived to first calving at 27mo of age. These animals were subsequently retained for an average of 2.75 lactations. Progeny were also included in the analysis, with bulls and heifers in excess of replacement requirements finished as grain-fed veal (270kg) at 6.5mo of age. All cattle were housed indoors and fed forages and grains produced on the same farm. Pre-farm gate GHG emissions and removals were quantified using Holos, a whole-farm software model developed by Agriculture and Agri-Food Canada and based on the Intergovernmental Panel for Climate Change Tier 2 and 3methodologies with modifications for Canadian conditions. The LCA yielded a GHG intensity of 0.92kg of CO(2) Eq/kg of fat- and protein-corrected milk yield. Methane (CH(4)) accounted for 56% of total emissions, with 86% originating from enteric fermentation. Nitrous oxide accounted for 40% of total GHG emissions. Lactating cows contributed 64% of total GHG emissions, whereas calves under 12mo contributed 10% and veal calves only 3%. Allocation of GHG emissions between meat and milk were assessed as (1) 100% allocation to milk, (2) economics, (3) dairy versus veal animals, and (4) International Dairy Federation equation using feed energy demand for meat and milk production. Comparing emissions from dairy versus veal calves resulted in 97% of the emissions allocated to milk. The lowest allocation of emissions to milk (78%) was associated with the International Dairy Federation equation. This LCA showed that greatest reductions in GHG emissions would be achieved by applying mitigation strategies to reduce enteric CH(4) from the lactating cow, with minimal reductions being achievable in young stock. Choice of coproduct allocation method can also significantly affect the relative allocation of GHG emissions to milk and meat.     

Towards a closed-loop cochlear implant system: application of embedded monitoring of peripheral and central neural activity

Although the cochlear implant (CI) is widely considered the most successful neural prosthesis, it is essentially an open-loop system that requires extensive initial fitting and frequent tuning to maintain a high, but not necessarily optimal, level of performance. Two developments in neuroscience and neuroengineering now make it feasible to design a closed-loop CI. One development is the recording and interpretation of evoked potentials (EPs) from the peripheral to the central nervous system. The other is the embedded hardware and software of a modern CI that allows recording of EPs. We review EPs that are pertinent to behavioral functions from simple signal detection and loudness growth to speech discrimination and recognition. We also describe signal processing algorithms used for electric artifact reduction and cancellation, critical to the recording of electric EPs. We then present a conceptual design for a closed-loop CI that utilizes in an innovative way the embedded implant receiver and stimulators to record short latency compound action potentials ( ~1 ms), auditory brainstem responses (1-10 ms) and mid-to-late cortical potentials (20-300 ms). We compare EPs recorded using the CI to EPs obtained using standard scalp electrodes recording techniques. Future applications and capabilities are discussed in terms of the development of a new generation of closed-loop CIs and other neural prostheses.     

Progress in AMS measurement of natural 32Si for glacier ice dating

AMS measurement of ³²Si can allow for ice core dating over the last thousand years. Technique developments are reported. Necessary negative-ion yields of 20–30% can now be consistently achieved, and permit an overall efficiency from ice sample to detector of ～1%. A ³⁰Si-spike technique has overcome the problem of extremely low intrinsic silicon concentration, with the added benefit of allowing determination of ppb-level silicon via isotope dilution. Improvements have also been made to the ionization detector in the gas-filled magnet that separates the accelerated ³²Si ions from the intense flux of ³²S ions. Preliminary ³²Si AMS results of snow and ice samples from Mt. Cook National Park, New Zealand, are reproducible, and with ³²Si concentrations 1.2–7.2 mBq/m³ comparable to results from mid-latitude snow samples measured previously via the radiometric technique, demonstrating the feasibility of the method. With these developments, the potential of ³²Si as ice core dating tool is close to being realized, and attempts to determine chronologies for both alpine and Antarctic glaciers are underway.     

Efficiency-limiting defects in silicon solar cell material

The precipitation rate of intentionally introduced iron during low-temperature heating is studied among a variety of single-crystal and polycrystalline silicon solar cell materials. A correlation exists between the iron precipitation rate and the carrier recombination rate in dislocation-free as-grown material, suggesting that diffusion-length-limiting defects in as-grown material are structural defects which accelerate iron precipitation. Phosphorous diffusion gettering was found to be particularly ineffective at improving diffusion length after intentional iron contamination in materials with high iron precipitation rates. We propose that intragranular structural defects in solar cell silicon greatly enhance transition metal precipitation during cooling from the melt and become highly recombination-active when decorated with these impurities. The defects then greatly impair diffusion length improvement during phosphorus gettering and limit carrier lifetimes in as-grown material.     

Preparations and reactions of quanternary salts of bis(chloromethyl) ether

The preparation of some novel quaternary salts of bis(chloromethyl) ether are described. The salts derived from trimethylamine are stable in alkali, whereas the ones containing pyridinium groups are unstable in alkali, and are formaldehyde donors and gelatin hardeners. A possible mechanism for the decomposition reaction is proposed.     

The selection and limitations of phenol as a reference toxicant to detect differences in sensitivity among groups of rainbow trout (Salmo gairdneri)

Phenol was better than sodium azide, sodium pentachlorophenate, copper sulphate and dodecylsodium sulphate in detecting differences in sensitivity among groups of rainbow trout (Salmo gairdneri). Phenol detected differences in sensitivity among strains of trout and could discern the effects of starvation, temperature stress and pre-exposure to 0.04 mg l⁻¹ chlorine on the sensitivity of trout to phenol, but not the effects of three brands of food and high mortality during holding. The sensitivity of rainbow trout to phenol was independent of weight and loading density in the bioassays. The use of phenol as a reference toxicant for the rapid detection of differences in sensitivity among groups of fish is limited because differences can only be detected by comparing the sensitivity of an unknown group of fish to that of a known, unstressed group of fish in the same bioassay. The concept of a single reference toxicant appropriate for bioassays with a variety of chemicals is questionable because differences among groups of fish, which are detectable by a reference toxicant, may not affect the results of bioassays with other chemicals. A series of physiological and behavioural screening tests and diagnostic health checks may be more useful than reference toxicants to identify groups of fish which should not be used in bioassays.