Oscillating superleak transducer of second sound: Amplitude and linewidth

Two oscillating superleak transducers, one serving as generator, the other as detector, of first and second sound, situated at opposite ends of a one-dimensional resonance cavity, are considered. Included in the analysis are the dissipative effects of normal viscous slip and thermal diffusion through the porous membrane. The calculated amplitude and linewidth of the receiver response, both close to and away from the membrane resonance, show good agreement with available experimental data.     

Enantiomer-based specificity in pheromone communication by two sympatricGnathoirichus species (Coleoptera: Scolytidae)

The aggregation pheromone ofGnathotrichus retusus was isolated and identified as (S)-(+)-sulcatol (6-methyl-5-hepten-2-ol). In laboratory and field experiments,G. retusus responded to (S)-(+)-sulcatol, but not to (±)-sulcatol, which was attractive to the sympatric species,G. sulcatus. G. sulcatus did not respond to optically pure (S)-(+)-sulcatol, but began to respond when 1% (R)-(–)-sulcatol was present in an enantiomeric mixture.Research supported by the National Science Foundation, U.S.A. (Grant BMS-74-13643), and the Natural Sciences and Engineering Research Council of Canada (Co-op grant A0243 and Operating Grant A3881 and A3785).     

Note: The intermodulation lockin analyzer

Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.     

Der Stand der Forschung zur Erfolgsmessung von Informationssystemen

Measuring information systems (IS) success is of great interest to both researchers and practitioners. This article examines multidimensional approaches to measuring IS success and explores the current state of IS success research through a literature review and by classifying articles published between 2003 and 2007. Based on a total of 41 academic journal and conference publications, the relevant research carried out is identified, while the research results are categorized, consolidated, and discussed. The results show that the dominant empirical research analyzes the individual impact of a certain type of information system by ascertaining users’ evaluation of it by means of surveys and then applying structural equation modeling. The DeLone and McLean Information Systems Success Model is the main theoretical basis of the reviewed empirical studies. This article provides researchers with a comprehensive review and structuring of IS success research. Furthermore, opportunities for additional development are identified and future research directions suggested.     

Resource-Bounded Measure and Learnability

We consider the resource-bounded measure of polynomial-time learnable subclasses of polynomial-size circuits. We show that if EXP ≠ MA, then every PAC-learnable subclass of P/poly has EXP-measure zero. We introduce a nonuniformly computable variant of resource-bounded measure and show that, for every fixed polynomial q , any polynomial-time learnable subclass of circuits of size q has measure zero with respect to P/poly. We relate our results to the question of whether the class of Boolean circuits is polynomial-time learnable. Received July 15, 1998, and in final form September 9, 1999.     

Investigating fuel-cell transport limitations using hydrogen limiting current

Reducing mass-transport losses in polymer-electrolyte fuel cells (PEFCs) is essential to increase their power density and reduce overall stack cost. At the same time, cost also motivates the reduction in expensive precious-metal catalysts, which results in higher local transport losses in the catalyst layers. In this paper, we use a hydrogen-pump limiting-current setup to explore the gas-phase transport losses through PEFC catalyst layers and various gas-diffusion and microporous layers. It is shown that the effective diffusivity in the gas-diffusion layers is a strong function of liquid saturation. In addition, it is shown how the catalyst layer unexpectedly contributes significantly to the overall measured transport resistance. This is especially true for low catalyst loadings. It is also shown how the various losses can be separated into different mechanisms including diffusional processes and mass-dependent and independent ones, where the data suggests that a large part of the transport resistance in catalyst layers cannot be attributed to a gas-phase diffusional process. The technique is promising for deconvoluting transport losses in PEFCs.     

Formulation effects on the distribution of pigment particles in paints

Modern water-borne paints are widely used in different areas of applications ranging from high-gloss lacquers to flat, scrub-resistant interior paints. From this point of view, the pigment volume concentration (PVC) is one key-parameter adjusting the desired application properties. In high-gloss paints, for example, a low PVC is required to accommodate the proper surface roughness to achieve a high gloss. Consequently, a high concentration of TiO₂ is needed to obtain a good hiding power at the same time. Flat paints nonetheless are highly filled due to cost reasons preferentially by CaCO₃ and the pigment binding capacity of the binder is crucial. In this work, paint formulations differing in PVC, and the type of binder or dispersing agent were investigated by various techniques concerning the distribution and aggregation of pigment particles, e.g. TiO₂. To get a detailed insight into the structure of the liquid paints and the corresponding dried paint films, suitable analytical tools were applied for characterization. The structure of the liquid paints was analyzed by remission light spectroscopy (RLS), disc centrifugation, cryogenic-replication transmission electron microscopy (Cryo-replica TEM) and cryogenic-scanning electron microscopy (Cryo-SEM). The pigment distribution in the corresponding dried paint films was examined by means of atomic force microscopy (AFM), TEM and RLS. The tendency of the TiO₂-pigments to form aggregates was found to depend on both: first on the type of binder used in the formulation and second on the employed dispersing agent. It is shown that only by adjusting the properties of the binder in combination with common dispersants, it is possible to get well-distributed TiO₂ particles within the paint. Correlation of application properties, e.g. gloss and blocking to the microscopic structure is presented.     

Thymic alterations in feline GM1 gangliosidosis

GM1 gangliosidosis is an inherited metabolic disease characterized by progressive neurological deterioration with premature death seen in children and numerous animals, including cats. We have observed that thymuses from affected cats greater than seven months of age (GM1 mutant cats) show marked thymic reduction compared to age-matched normal cats. The studies reported here were done to describe alterations in the thymus prior to (less then 90 days of age) and during the development of mild (90 to 210 days of age) to severe (greater than 210 days of age) progressive neurologic disease and to explore the pathogenesis of the thymic abnormality. Although histologic examination of the thymus from GM1 affected cats less than 210 days of age showed no significant differences from age-matched control cats, thymuses from GM1 mutant cats greater than 210 days of age were significantly reduced in size (approximately 3-fold). Histologic sections of lymph nodes, adrenal glands, and spleens from GM1 gangliosidosis-affected cats showed no significant differences. Flow cytometric analyses showed a marked decrease in the percentage of immature CD4+CD8+ thymocytes (p < 0.001) and significantly increased CD4-CD8+ cells (p < 0.01) in GM1 mutant cats greater than 210 days of age when compared to normal age matched cats. Co-labelling with CD4, CD8, and CD5 indicated an increase in the percentage of GM1 mutant cat thymocytes at this age which were CD5high, suggesting the presence of more mature cells. Cytometric analyses of subpopulations of peripheral lymphocytes indicated an increase in CD4-CD8+ cells (p < 0.05) with concurrent decreases in CD4+CD8- and CD4-CD8- cells (which were not significant). Similar analyses of thymocyte and lymphocyte subpopulations from cats < 210 days of age showed no significant differences between GM1 mutant and normal cells. GM1 mutant cats at all ages had increased surface binding of Cholera toxin B on thymocytes, indicating increased surface GM1 ganglioside expression. Increases were highly significant in GM1 mutant cats greater than 210 days of age. In situ labelling for apoptosis was increased in GM1 mutant cats between 90 to 200 days of age when thymic masses were within normal limits. In GM1 mutant cats over 200 days of age, decreased labelling was observed when thymic mass was reduced and the CD4+CD8+ subpopulation, known to be very susceptible to apoptosis, was significantly decreased. These data describe premature thymic involution in feline GM1 gangliosidosis and suggest that increased surface GM1 gangliosides alters thymocyte development in these cats.     

An amorphous silicon thin film transistor: Theory and experiment

The volt-ampere characteristics for a thin film transistor fabricated with vacuum deposited amorphous silicon as the semiconductor is presented. The substrate is single crystalline silicon with a 3000 Å layer of thermally grown silicon dioxide as the insulator. The gate is a buried N⁺ phosphorus diffused region while the source and drain contacts are interdigited fingers of aluminum. By using the Cohen-Fritzsche-Ovshinsky model for the density of localized states in the mobility gap, the V_G vs I_D characteristic at small values of V_D is predicted and experimentally verified. This characteristic is used to theoretically predict the family of I_D curves for the TFT over a range of V_G and V_D. The theory and experiment agree exceptionally well below the gate-drain pinch-off, thereby verifying the theory of a TFT with a uniform distribution of traps in the band-gap.