Dual mirror and resonant cavity operating at 1.3 and 1.55 μm

A GaAs/AlAs Bragg mirror with two reflectivity bands centred at 1.3 and 1.55 μm is reported. High reflectivity is achieved in both bands and good agreement is observed between measured and simulated reflectivities. A microcavity structure is proposed that is resonant at both wavelengths. Such structures can be used to enhance the absorption or emission of signals at the two wavelengths     

Using rule induction for knowledge acquisition: An expert systems approach to evaluating material errors and irregularities

There has been a significant increase in the magnitude of material errors discovered in financial statements during the 1980s. Auditors, financial analysts, and regulators have shown considerable interest in evaluating and predicting these material errors. This paper describes the development and validation of a prototype expert system, ERRORXPERT, which evaluates material errors and potential fraud. This prototype system is designed to assist auditors at the planning stage in the design of subsequent substantive tests, when material errors and irregularities in the financial statements are probable. A commercial machine learning program was used for rule induction. A set of training examples comprising error and non-error firms was used to generate rules and a separate holdout sample was used to validate the expert system results. The performance of the expert system was also compared to that of a multiple discriminant analysis model using the same data. The results demonstrate that the expert system, ERRORXPERT, outperforms the discriminant model and is a powerful evaluation tool to classify firms into error and non-error categories. The size of the sample used in this study somewhat limits the generalizability of the specific rules.     

Activation and characterization of Fe---Mn---SO4/ZrO2 catalysts

Changes in Fe---Mn---SO₄²⁻/ZrO₂ catalyst formulations during activation have been observed. In air or an inert gas, the added salt, such as iron and/or manganese nitrate, decomposes over a temperature range of about 200–400°C to produce nitric oxide, oxygen and iron and/or manganese oxide. The crystallization of zirconia occurs at 450°C; when the sample contains sulfate the exothermic event occurs at a temperature that is about 200°C higher. Heating in the presence of hydrogen causes the evolution of nitric oxide to occur over a narrow temperature range and at a lower temperature than when the sample is heated in helium or air. It appears that the nitrate ions associated with Fe, Mn and Zr decompose to produce nitric oxide, and presumably water, at different temperatures when the sample is heated in the presence of hydrogen. Heating samples of sulfated zirconia containing iron and/or manganese in hydrogen causes sulfur evolution at a lower temperature, and a significant fraction of it in the form of H₂S.     

Disruption of three phosphatidylinositol-polyphosphate 5-phosphatase genes from Saccharomyces cerevisiae results in pleiotropic abnormalities of vacuole morphology, cell shape, and osmohomeostasis

We have shown previously that switching of the alpha v-associated beta1 and beta5 integrin subunits during differentiation of myelin-forming oligodendrocytes may regulate important aspects of cell behaviour such as migration (Milner et al., 1996: J Neurosci 16:7240-7252). In this study we have examined the developmental regulation of other alpha v-associated beta subunits in oligodendroglial cell cultures and also the control of their expression by neurons, using xenocultures to distinguish glial and neuronal integrins. We have found that oligodendroglia express alpha vbeta8 in addition to the previously-described alpha vbeta1, alpha vbeta3, and alpha vbeta5. Beta8 and beta3 together comprise the 80kD band seen in alpha v immunoprecipitations that represents the most abundant alpha v-associated beta subunit and show reciprocal patterns of expression during development. Alpha vbeta8 is expressed at high levels on oligodendrocyte precursors and differentiated oligodendrocytes but diminishes during the intermediate stages of differentiation. Alpha vbeta3, in contrast, shows an opposite pattern of expression, with the highest levels seen at the intermediate stages of differentiation and little expression on either oligodendrocyte precursors and differentiated oligodendrocytes. The expression of alpha vbeta3 is not altered by coculture with neurons, unlike that of alpha vbeta8, in which the decrease seen at the intermediate stages of differentiation is less marked in the presence of neurones. Our results confirm that switching of alpha v-associated beta subunits is an important feature of oligodendrocyte differentiation and suggest that alpha vbeta8 and alpha vbeta3 have distinct functions during myelination.     

Micro-level energy planning in India—A case study of bangalore north Taluk

Demand for energy in India is constantly on the rise and the conventional supply options available have failed to cope with this increase. The emergence of efficiency improvement, carrier substitution and renewable energy as alternative sources of energy supply, make adherence only to macro-level energy planning unrealistic. A micro-level (district/taluk) energy planning becomes pragmatic under these circumstances to pursue the goal of sustainable development and to harness locally available energy resources. This paper considers the energy consumption pattern in Bangalore North taluk in 1987–88 and projects the demand for energy in 1995–96. Taking into account the different energy sources used to provide different end-use services through different end-use devices, the paper presents a linear programming formulation for optimum allocation. The model considers the conventional and new alternative technologies for meeting the demand for energy service. The results show that substantial savings could be achieved by this optimal allocation. The cost savings could be to the tune of Rs 41.879 million in Bangalore North taluk during 1995–96 (terminal year of Eighth Five-Year Plan). Energy savings of about 27% and cost savings of 16% could also be achieved.     

Uniform discrimination of pattern orientation by honeybees

To explore how honeybees, Apis cerana, discriminate the orientation of patterns, we trained workers to discriminate between a black stripe of a certain orientation on a white disc and a pure white disc. We tested trained bees for their ability to discriminate between the trained orientation and deviations from it. This was done either in a dual choice situation where the bees had to choose between the trained orientation and one deviation from it at a time, or in a multiple choice situation where bees had to choose simultaneously between the trained orientation and 11 successive deviations from it. In the dual choice situation, bees did not discriminate behaviourally between the trained orientation and deviations up to 25 degrees, whereas in a multiple choice situation, they discriminated between the trained orientation and a deviation of 15 degrees or more. Thus, orientation can be analysed more precisely in multiple choice experiments. The response of the bees was independent of the orientation of the trained orientation; the 12 different trained orientations all yielded identical results. This finding, considered together with a model that we present for orientation discrimination, suggests that at least three orientation-sensitive channels (a neuron or a set of neurons that respond maximally to a particular orientation) participate in the analysis of pattern orientation. (c) 1998 The Association for the Study of Animal Behaviour.     

Polyaniline-based nanocomposite materials for hydrogen storage

Nanomaterials have diverse tunable physical properties as a function of their size and shape due to strong quantum confinement effect and large surface to volume ratio. On basis of these facts, nanocomposite materials can be considered as strong candidates for hydrogen storage. In the present work, we report a novel conducting polymeric nanocomposite material for hydrogen storage. Conducting polymer-based nanocomposites were modified using carbon nanotubes as filler material. This further increased the porous structure of the nanocomposite and the number of binding sites, which in turn enhances the hydrogen storage capacity. Additionally, fine aluminum powder was added to the polymeric nanocomposite, which further increased the hydrogen sorption of the material. The modified conducting polymeric nanocomposites were characterized with various analytical techniques including FTIR, DSC, TGA and SEM. Adsorption and desorption experiments are conducted using a Sieverts-type volumetric PCT instrument. Further experiments are in progress to understand the hydrogen storage mechanism in the proposed conducting polymer nanocomposites.     

A convenient method for affinity purification of maltose binding protein fusions

We identified a novel heterodimeric protein, lipophilin AC, in human tears. One of its components, lipophilin A (69 residues; mass, 7575.1; pI, 9.47) was homologous to the C1 and C2 components of prostatein ('estramustine-binding protein'), the major secreted protein of rat prostate. Human lipophilin C (77 residues; mass, 8854.1; pI, 4.94) was homologous to the rat prostatein C3 component and to human mammaglobin, a protein overexpressed in some mammary carcinomas. Tear lipophilins A and C expand the roster of human uteroglobin superfamily members and provide models for exploring these typically steroid-regulated and steroid-binding molecules.     

Xunet 2: lessons from an early wide-area ATM testbed

This paper is a retrospective on the design of Xunet 2, one of the earliest functional wide-area asynchronous transfer mode (ATM) networks. Work on Xunet 2 began in 1989 and the network, consisting of experimental ATM switches, IP routers, and 45 Mb/s transmission lines, has been operational since October 1991. The network serves as a “laboratory without walls” for eight research groups across the United States. While Xunet 2 has only a small number of nodes, it was designed as a prototype of a nationwide ATM network. This paper reviews some of the design decisions and lessons learned in the project and points out the research directions motivated by this work, focusing on the areas of traffic management, ATM switch design, network control, and the implementation of an IP router