Software verification effort at the MIMICAD center for microstrip passive components

A software verification effort to verify the accuracy of the simulation program developed by the Center for Microwave/Millimeter-Wave Computer-Aided Design (MIMICAD) is described. A set of single-layer microstrip structures selected by the MIMICAD sponsors were fabricated on GaAs substrates for testing purposes. Ranging from an interdigitated capacitor to radial stubs to a section of meander line, these test structures are components commonly used in MMIC designs. Round-robin measurements of the test structures were carried out among the MIMICAD sponsors to assess measurement consistency. Comparisons between the measured and simulated results as well as the effect of discretization in the simulation process are discussed.     

Separation von Starterkulturen nach Hochdruck‐Homogenisierung

The present work demonstrates how shearing through a high‐pressure homogenizer affects the separation properties of exopolysaccaride producing bacterial starter cultures. In addition to changes in medium viscosity and sedimentation velocity significant differences in the compactness of the cell sediment were observed. The scalability of the laboratory results obtained through analytical centrifugation in larger scale using a stack disc separator is also demonstrated.     

A multi-level approach to ubiquitous modeling and solving constraints in combinatorial optimization problems in production and distribution

Constraints, although ubiquitous in production and distribution planning, scheduling and control, often lead to inconsistencies in the decision-making process. The constraint-based modeling helps circumvent many organization-impacting issues. To address this, we developed a multi-level approach to the modeling and solving of combinatorial optimization problems. It is versatile and effective owing to the use of multi-level presolving and multiple paradigms, such as constraint programming, logic programming, mathematical programming and fuzzy logic, for their complementary strengths. The capability of this framework and its advantage over mathematical programming alone or over hybrid frameworks is shown in the illustrative example, in which combinatorial optimization is used as a benchmark to prove the effectiveness of the proposed approach. Knowledge of the problem is stored in the form of facts.     

Subsurface hardening in erosion-damaged copper as inferred from the dislocation cell structure,and its dependence on particle velocity and angle of impact

Previously published measurements of the cell diameters d of dislocation cells underneath copper surfaces exposed to particle erosion were evaluated in terms of the subsurface stresses τ to which they correspond. These were compared with the elastic stresses expected underneath spherical indenters impacting on the surface with different speeds. The inferred stresses differ markedly from theoretical predictions, not only in regard to the dependence on speed and angle of impact but even in regard to their decay along the z axis, the direction normal to the surface. Instead of τ decreasing as z^?n with n continuously rising from 0 at a shallow depth to 2 at large depths, as predicted from elastic theory, the stresses follow a z^?1 dependence throughout the measured range. All data are satisfactorily explained by the relationship $\text{1/d = (7/z)v}{}^{\mathrm{<mtext>2</mtext><mtext>5</mtext>}}\text{sin α ≈ τ/100}$ (using MKS units), where v stands for the velocity of the impacting particles, namely rather irregularly shaped alumina particles 50 μm in diameter, and α is the angle of impact. No theoretical explanation has so far been found to account for this result. It is noted, however, that previously a z^?1 decay of stress had already given excellent results in a theoretical interpretation of the subsurface shear strain underneath a surface subject to sliding wear. Further, sin α is the direction cosine for the normal force component, whereas a velocity dependence of $\text{v}{}^{\mathrm{<mtext>2</mtext><mtext>5</mtext>}}$ is found from elastic theory for the depth scaling of the elastic stress due to a spherical indenter. Suggestions are made for further experiments.     

A novel test approach for plasma-sprayed coatings tested simultaneously under CMAS and thermal gradient cycling conditions

Plasma-sprayed ceramic coatings, used as thermal barrier or abradable coatings in high-pressure stages of gas turbines, are exposed to high thermo-mechanical loading due to harsh operating conditions. Under certain conditions they also have to withstand attack by calcium-magnesium-alumino-silicate (CMAS) deposits resulting from the ingestion of siliceous minerals with the intake air.Resistance to this kind of attack becomes more important at higher temperatures, when the melting temperature of the CMAS deposits is exceeded and a penetration into the coating microstructural features (cracks and pores) can take place. During cooling the CMAS solidifies and the coating loses its strain tolerance, which can lead to coating failure. Although the basic principles of failure seem to be understood, a detailed analysis of the mechanisms and the possibilities of avoiding delamination are still lacking, especially because there are as yet no adequate test beds.This paper investigates the possibility of testing such coatings in a burner rig test facility under thermal gradient cycling conditions and at the same time CMAS deposition. This novel and unique test approach promises a coating screening and characterization test under service conditions. The CMAS rig was established because the test conditions simulated here are closer to actual engine conditions, as compared to previous tests with primarily CMAS deposition and subsequent thermal furnace testing.The experimental setup of this new test approach is described and the applicability is confirmed. Furthermore, a first evaluation for plasma-sprayed coatings is presented. A significantly reduced lifetime was found for samples tested with CMAS attack in comparison to tests with water deposition only. The lifetime was also reduced compared to older results without any corrosive media. A decrease of nearly two orders of magnitude was found. A microstructural evaluation of the coatings is presented and the mechanisms and reasons for the very early failure are discussed.     

Development of Oxide Scale at 1,100 °C on Fe20Cr5Al Alloy Non-Implanted and Yttrium-Implanted

The development of the oxide scale on model Fe20Cr5Al-type alloys unmodified and containing implanted yttrium was studied in oxygen-dominated atmosphere at 1,100 °C for up to 1 h. A two-stage-oxidation exposure was applied with the use of ¹⁸O₂ as a tracer. The choice of the exposure durations ensured the possibility to follow the consecutive stages of scale development. The oxidized samples were characterized using SEM (morphology); PLS (phase composition), and SIMS (elemental distributions). The obtained results are discussed in terms of the mechanism of the development of protective α-Al₂O₃ scale and the effect of the additions on this process taking into account the necessity of distinguishing the mechanism and kinetics of the scale evolution. Similar scale evolution stages were found on both studied materials and in both cases the protective α-Al₂O₃ scale developed rapidly, already after the exposure for 3 min. Implanted yttrium appeared to have a negligible effect on the evolution of the scale. It only slightly retarded the evolution which can be attributed rather to a kinetic effect than to mechanistic one. However, the mechanical failure of the scales via formation of cracks at the asperities of convolutions occurred on the yttrium-implanted alloy but not on the non-implanted one.     

Oxidation of Various Kraft Lignins with a Bacterial Laccase Enzyme

Modification of kraft lignin (KL), traditionally uses harsh and energy-demanding physical and chemical processes. In this study, the potential of the bacterial laccase CotA (spore coating protein A) for oxidation of KL under mild conditions was assessed. Thereby, the efficiency of CotA to oxidize both softwood and hardwood KL of varying purity at alkaline conditions was examined. For the respective type of wood, the highest oxidation activity by CotA was determined for the medium ash content softwood KL (MA_S) and the medium ash content hardwood KL (MA_H), respectively. By an up to 95% decrease in fluorescence and up to 65% in phenol content coupling of the structural lignin units was indicated. These results correlated with an increase in viscosity and molecular weight, which increased nearly 2 and 20-fold for MA_H and about 1.3 and 6.0-fold for MA_S, respectively. Thus, this study confirms that the CotA laccase can oxidize a variety of KL at alkaline conditions, while the origin and purity of KL were found to have a major impact on the efficiency of oxidation. Under the herein tested conditions, it was observed that the MA_H KL showed the highest susceptibility to CotA oxidation when compared to the other hardwood KLs and the softwood KLs. Therefore, this could be a viable method to produce sustainable resins and adhesives.     

Influence of polymeric flame retardants based on phosphorus‐containing polyesters on morphology and material characteristics of poly(butylene terephthalate)

Flame retarded poly(butylene terephthalate) (PBT) is required for electronic applications and is mostly achieved by low molar mass additives so far. Three phosphorus‐containing polyesters are suggested as halogen‐free and polymeric flame retardants for PBT. Flame retardancy was achieved according to cone calorimeter experiments showing that the peak heat release rate and total heat evolved were reduced because of flame inhibition and condensed‐phase activity. The presented polymers containing derivatives of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide form immiscible blend systems with PBT. Shear‐rheology shows an increase in storage moduli at low frequencies. This is proposed as quantitative measure for the degree of phase interaction. The phase structure of the blends depends on the chemical structure of the phosphorus polyester and was quite different, depending also on the viscosity ratio between matrix and second phase. A lower viscosity ratio leads to two types of phases with spherical and additionally continuous droplets. Addition of the flame retardants showed no influence on the dielectric properties but on the mechanical behavior. The polymeric flame retardants significantly diminish the impact strength because of several reasons: (1) high brittleness of the phosphorus polyesters themselves, (2) thermodynamic immiscibility, and (3) weak phase adhesion. By adding a copolymer consisting of the two base polymers to the blend, an improvement of impact strength was obtained. The copolymer particularly acts as compatibilizer between the phases and therefore leads to a smaller phase size and to a stronger phase adhesion due to the formation of fibrils. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013