Composing, analyzing and validating software models to assess the performability of competing design candidates

In a perfect world, verification and validation of a software design specification would be possible before any code was generated. Indeed, in a perfect world we would know that the implementation was correct because we could trust the class libraries, the development tools, verification tools and simulations, etc. These features would provide the confidence needed to know that all aspects (complexity, logical and timing correctness) of the design were fully satisfied (i.e., everything was right). Right in the sense that we built it right (it is correct with respect to its specification) and it solves the right problem. Unfortunately, it is not a perfect world, and therefore we must strive to continue to refine, develop and validate useful methods and tools for the creation of safe and correct software. This paper considers the analysis of systems expressed using formal notations. We introduce our framework, the modeling cycle, and motivate the need for tool supported rigorous methods. Our framework is about using systematic formal techniques for the creation and composition of software models that can further enable reasoning about high‐assurance systems. We describe several formal modeling techniques within this context (i.e., reliability and availability models, performance and functional models, performability models, etc.). This discussion includes a more precise discourse on stochastic methods (i.e., DTMC and CTMC) and their formulation. In addition, we briefly review the underlying theories and assumptions that are used to solve these models for the measure of interest (i.e., simulation, numerical and analytical techniques). Finally, we present a simple example that employs generalized stochastic Petri nets and illustrates the usefulness of such analysis methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Zeolite HNU-87: synthesis, characterization and catalytic properties in the shape-selective conversion of methylnaphthalenes

The synthesis of the high-silica zeolite NU-87 and its physicochemical characterization are reported. The catalytic properties of zeolite HNU-87 were investigated in the conversion of 1- and 2-methylnaphthalene. Both isomerization to the corresponding methylnaphthalene and transalkylation to naphthalene and dimethylnaphthalenes are observed. The influence of reaction temperature and the modified residence time on the product distributions is reported and discussed in terms of shape selectivity effects in the peculiar pore system of NU-87. For comparison, typical results obained with zeolite HMCM-22, which possesses a similar pore architecture, are also included. The results of methylnaphthalene conversion over HNU-87 are compared to those obtained in the alkylation of naphthalene with methanol on the same zeolite catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

3-D surface analysis of worn spherical roller thrust bearings

Wear of boundary lubricated spherical roller thrust bearings has been characterised with 3-D surface measurements and analysis. Due to the curved contact surface in a spherical roller thrust bearing, the rollers will undergo sliding in the contact. For an unskewed roller there will be two points along each contact where the sliding velocity is zero. At all other points along the contact, sliding is present. Previously presented results from measurements of the contacting surfaces show that outside the zero sliding points there is a significant change in the washer surface profile due to wear. In order to study how the wear depends on the number of revolutions ten tests were performed. After the tests, 3-D surface roughness measurements were performed. The results from these measurements show that there are different wear mechanisms involved. Initially, the surfaces are run in by possible plastic deformation and two-body abrasion. After running-in, the surfaces are subjected to mild wear probably caused by two-body abrasion and/or delanunation wear. For the long term tests, three-body abrasion clearly influences the amount of wear. A 3-D parameter set was used to characterise the different wear mechanisms. Three amplitude parameters (S_a, S_q S_z) and three of the functional Abbot curve parameters (S_pk, S_k, S_vk) were able to characterise all the wear mechanisms.     

Nanoscale Indentation and Scratch of Short Carbon Fiber Reinforced PEEK/PTFE Composite Blend by Atomic Force Microscope Lithography

The atomic force microscope (AFM) has become a popular tool for characterizing surfaces of different types of materials. In this paper a new technology of AFM–SPM lithography was used to conduct nanoscale scratch and indentation tests on a short carbon fiber reinforced PEEK/PTFE composite blend. In the scratch test, by moving the tip across the surface at constant velocity and fixed applied force, grooves with nanometer scale dimensions were fabricated on the PEEK matrix surfaces. The grooves consisted of a central trough with pile-ups on each side. These grooves provided information about deformation mechanisms and scratch resistance of the individual phases. In the nanoscale indentation and scratch of the polymeric phases, microploughing and microcutting are the dominant wear mechanisms. The harder phases, i.e., graphite and carbon fibers, get worn by microcracking events.     

Catalysis with Soluble Hybrids of Highly Branched Macromolecules with Palladium Nanoparticles in a Continuously Operated Membrane Reactor

The continuous recovery and recycling of soluble metal nanoparticles by means of ultrafiltration is described, employing hybrids of palladium nanoparticles with highly branched amphiphilic polyglycerol as a catalyst for cyclohexene hydrogenation as a model reaction. In a continuously operated membrane reactor a productivity of 29000 TO over 30 exchanged reactor volumes was observed for nanoparticles of 2.2 nm size, with a maximum rate of 1200 TO h⁻¹. Catalysis by soluble metal complexes can be excluded. After 30 hours of operation, some decrease in activity is observed which is due to deposition of palladium on the ultrafiltration membrane, however this material does not contribute to catalytic activity.     

The use of new blockcopolymeric dispersing agents for waterborne paints — theoretical and practical aspects

Newly developed blockcopolymeric dispersing agents are evaluated in their performance with a number of pigments in order to obtain a deeper understanding of the dispersing process and of the factors that affect the stability of waterborne binder free pigment concentrates. Special attention is paid to the variation of the amphiphilic ionic/non-ionic and hydrophobic/hydrophilic properties of these new dispersants. By measuring particle surface charges and particle size distributions of pigment pastes and by determining relevant properties of the films obtained after application the effect of a number of binders and other paint components on the stability of dispersions is also evaluated. Guidelines for efficient and economically optimum preparation of pigmented waterborne paints are given.     

In-line measurement of tempered cocoa butter and chocolate by means of near-infrared spectroscopy

In the present work cocoa butter and chocolate were precrystallized by means of a newly developed shear crystallizer. The shear crystallizer was integrated into a circular loop. The handling of precrystallized cocoa butter showed a high dependency on the timing of applied analysis. Differential scanning calorimetry, calorimetry, rheometry, and in-line near-infrared (NIR) were all directly influenced by the fat crystal structure. Nevertheless, for cocoa butter it was shown that mechanical energy input (rpm) had a significant influence on viscosity, melting enthalpy, and slope at the second point of inflection of a temper curve. Experiments with cocoa butter at constant exit temperature showed a linear increase of viscosity between 0.1 and 0.8 Pa·s in the range of 300 to 1300 rpm. Melting enthalpy increased in the same rpm interval from 0.02 to 2.5 J/g. Solidification time (from 4.5 to 0.5 min) and slope (from 0.82 to 0.15, second point of inflection of temper curve) consequently decreased (both with exponential approximation). For cocoa butter, slope and solidification time correlated linearly whereas solidification time and viscosity followed a power law fit. This proved that defined relationships exist between rheological data and data from temper curve measurements. Viscosity was linearly dependent on crystal content. By means of NIR spectroscopy good correlation models for cocoa butter viscosity, enthalpy (crystal content), and slope values were found. For precrystallized chocolate, analytical values such as viscosity and slope values were detected off-line and used for calibration of NIR spectroscopy.     

Characterization of forced oxidation of sardine oil: Physicochemical data and mathematical modeling

It is of major interest to the food industry to understand the mechanisms and kinetics underlying spontaneous oxidation of marine oils because these polyunsaturated fatty acid (PUFA)-rich oils, the object of several health claims, have been repeatedly recommended for dietary intake. The present study attempts to characterize forced oxidation and hydrolytic breakdown of glycerides and fatty acids in sardine oil. A simple, first-order mathematical model was postulated and successfully fitted to the experimental data. This model confirmed that the rate of decrease in concentration of intact fatty acid moieties is almost directly proportional to the number of double bonds present. Therefore, as expected, the rate of oxidative decay was virtually independent of chain length, with an overall activation energy of ca. 22 kJ mol⁻¹. Additionally, the rate of hydrolysis was correlated with the rate of oxidative decay. With the exception of fatty acids possessing more than four double bonds, PUFA proved to be relatively stable to oxidation for up to 10 h at 50–70°C, and the qualitatively richest pattern of volatiles was obtained when the reaction was performed at the highest temperature (80°C).