Microwave Cavity Perturbation as a Tool for Laboratory In Situ Measurement of the Oxidation State of Three Way Catalysts

Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today’s emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by H₂O and CO₂. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects.     

Matching large color differences with achromatic and chromatic surrounds

A color-difference-matching experiment was carried out using a computer-interfaced video-display system. Two reference color stimuli (i) and (j), and one test stimulus (i,j) surrounded by a large achromatic or chromatic stimulus were presented on the video screen. An observer was asked to adjust the test stimulus until he perceived it to have a color precisely “half way” between the colors of the given reference stimuli. A satisfactory half-way color was the one that produced perceptually equal color differences between (i) and (i,j) and (j) and (i,j) and simultaneously made these color differences as small as possible. Although the given color difference between the test stimuli (i) and (j) was generally quite large (100–200 just-perceptible color-difference steps) with the achromatic surround condition, the color-difference matching required to obtain the desired half-way color did not present any serious difficulties to the observer. The uncertainty of the chromaticity point of the half-way color was established by an ellipse of small to moderate size surrounding the mean chromaticity setting. The orientation and shape of the uncertainty ellipse was comparable with the orientation and shape of uncertainty ellipses obtained by other investigators studying color-difference matching involving much smaller color differences. The unexpected and noteworthy result of the present study lies in the location of the chromaticity point of (i,j) relative to those of (i) and (j) as a function of surround color. The location of (i,j) depends on the saturation of the surround stimulus but not its hue. Some speculative explanations of the observed results are offered.     

Compositional message sequence charts

A message sequence chart (MSC) is a standard notation for describing the interaction between communicating objects. It is popular among the designers of communication protocols. MSCs enjoy both a visual and a textual representation. High-level MSCs (HMSCs) allow specifying infinite scenarios and different choices. Specifically, an HMSC consists of a graph, where each node is a finite MSC with matched send and receive events, and vice versa. In this paper we demonstrate a weakness of HMSCs, which disallows one to model certain interactions. We will show, by means of an example, that some simple finite state communication protocol cannot be represented using HMSCs. We then propose an extension to the MSC standard which allows HMSC nodes to include unmatched messages. The corresponding graph notation will be called HCMSC, which stands for high-level Compositional message sequence charts. With the extended framework, we provide an algorithm for automatically constructing an MSC representation for finite state asynchronous message passing protocols.     

Global extensional assertions and local integrity constraints in federated schemata

Integrated access to multiple data sources requires a homogeneous interface provided by a federated schema. Such a federated schema should correctly reflect the semantics of the component schemata of which it is composed. Since the semantics of a database schema is also determined by a set of semantic integrity constraints, a correct schema integration has to deal with integrity constraints existing in the different component schemata. Traditionally, most schema integration approaches solely concentrate on the structural integration of given database schemata. Local integrity constraints are often simply neglected. Their relationship to global extensional assertions, which form the basic integration constraints, are even ignored completely. In this paper, we discuss the impact of global extensional assertions and local integrity constraints on federated schemata. In particular, we point out the correspondence between local integrity constraints and global extensional assertions. The knowledge about the correspondences between the given integrity constraints and extensional assertions can then be utilized for an augmented schema integration process.     

Formation of Mullite from Filled Siloxanes

Monolithic mullite with low sintering shrinkage was synthesized from polymer/filler blendsMthat is, siloxane/alumina (siloxane/Al₂O₃) (and siloxane/aluminum (siloxane/Al)) mixtures. The synthesis was based on a reaction-bonding process of amorphous silica, which formed when the siloxane was oxidized, with Al₂O₃ (or oxidized aluminum filler) at temperatures >1250°C. Thermodynamic calculations were used to calculate the phase composition at equilibrium. Thermoanalytical, infrared-spectroscopic, and microscopic techniques were applied to reveal the microstructural evolution. The corresponding volume changes were used to evaluate the linear shrinkage, based on the quantitative phase assemblage.     

Lorentz force influence on momentum and mass transfer in natural convection copper electrolysis

The influence of Lorentz forces generated by faradaic currents and magnetic fields from permanent magnets on the momentum and mass transfer in natural convection copper electrolysis is discussed. Flow field measurements and visualizations of the concentration distribution are given and related to measured mean current densities. Flow structure as well as mass transfer depend strongly on the direction of the Lorentz force relative to that of natural convection.     

Polymerization mechanisms and molecular weight distributions. III. Gamma-radiation-initiated polymerization of methyl methacrylate

The termination mechanism in gamma-radiation-initiated polymerization of methyl methacrylate was investigated. The termination mechanism and the associated rate constants were determined by comparing the theoretical molecular weight distribution (MWD) and the experimental MWD, which was determined by gel permeation chromatography. Disproportionation occurs 1.2 times as frequently as combination at 30°C and 0.5 times as frequently at 0°C. The activation energy for disproportionation is 5.5 kcal/mole greater than that for combination. The rates of initiation were determined by a new method and were found to compare well with those reported in the literature. It is also suggested that it is necessary for the theoretical MWD to have the same shape as the experimental MWD before a mechanism can be authenticated.     

Effect of α to β (β') Phase Transition on the Sintering of Silicon Nitride Ceramics

By using α-Si₃N₄ and β-Si₃N₄ starting powders with similar particle size and distribution, the effect of α-β (β') phase transition on densification and microstructure is investigated during the liquid-phase sintering of 82Si₃N₄·9Al₂O₃·9Y₂O₃ (wt%) and 80Si₃N₄·13Al₂O₃·5AIN·5AIN·2Y₂O₃. When α-Si₃N₄ powder is used, the grains become elongated, apparently hindering the densification process. Hence, the phase transition does not enhance the densification.     

High-finesse laterally coupled organic-inorganic hybrid polymer microring resonators for VLSI photonics

We produced laterally coupled optical microring resonators having high finesse (F/spl sime/17 at 1.5-/spl mu/m wavelength) using a two-step patterning technique based on optical photolithography. The technique used allows us to separately control the height of both ring and port waveguides and structure submicrometer gaps. The resonance spectrum of microrings with radii of 50 /spl mu/m made of an organic-inorganic hybrid polymer have an extinction ratio of about 12 dB and a filter bandwidth /spl delta//spl lambda//spl sime/0.28 nm (full-width at half-maximum) at a wavelength /spl lambda/=1547.78 nm. We show that the resonances can be thermooptically tuned by 0.2 nm//spl deg/C, thus allowing us to modulate the transmission of the through port signal.     

The Active Vertice method: a performant filtering approach to high-dimensional indexing

The problem of finding nearest neighbors has emerged as an important foundation of feature-based similarity search in multimedia databases. Most spatial index structures based on the R-tree have failed to efficiently support nearest neighbor search in arbitrarily distributed high-dimensional data sets. In contrast, the so-called filtering principle as represented by the popular VA-file has turned out to be a more promising approach. Query processing is based on a flat file of compact vector approximations. In a first stage, those approximations are sequentially scanned and filtered so that in a second stage the nearest neighbors can be determined from a relatively small fraction of the data set.

In this paper, we propose the Active Vertice method as a novel filtering approach. As opposed to the VA-file, approximation regions are arranged in a quad-tree like structure. High-dimensional feature vectors are assigned to ellipsoidal approximation regions on different levels of the tree. A compact approximation of a vector corresponds to the path within the index from the root to the respective tree node. When compared to the VA-file, our method enhances the discriminatory power of the approximations while maintaining their compactness in terms of storage consumption. To demonstrate its effectiveness, we conduct extensive experiments with synthetic as well as real-life data and show the superiority of our method over existing filtering approaches.