Mechanical properties of wollastonite‐reinforced polypropylene composites modified with SEBS and SEBS‐g‐MA elastomers

Mechanical properties of isotactic polypropylene/wollastonite/styrene rubber block copolymers (iPP/wollastonite/SRBC) composites were studied as a function of elastomeric poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) triblock copolymer (SEBS) and SEBS grafted with maleic anhydride (SEBS‐g‐MA) content from 0 to 20 vol%. Microphase morphology was stronger influenced by SRBC elastomers than by different wollastonite types. Higher encapsulation ability of SEBS‐g‐MA than SEBS caused more expressive core‐shell morphology and consequently higher notched impact strength as well as yield parameters, but lower Young's modulus. Higher ductility of the composites with SEBS than with SEBS‐g‐MA has been primarily caused by better miscibility of the polypropylene chains with SEBS molecules. Surface properties of components and adhesion parameters also indicated that adhesion at SEBS‐g‐MA/wollastonite interface, which was stronger than the one at the SEBS/wollastonite interface, influenced higher encapsulation of wollastonite particles by SEBS‐g‐MA. POLYM. ENG. SCI., 47:1873–1880, 2007. © 2007 Society of Plastics Engineers     

Structure Development of NiO–YSZ Oxide Mixtures in Simulated Citrate–Nitrate Combustion Synthesis

Yttria-stabilized zirconia (NiO/YSZ) composites were prepared by the modified citrate–nitrate combustion synthesis. The citrate–nitrate combustion proceeded through several consecutive steps. Evolution of structure in the system and its changes were followed up by thermogravimetry-differential scanning calorimetry, X-ray powder diffraction, extended X-ray absorption fine structure, and high resolution transmission electron microscopy analyses of intermediate products prepared at distinct temperatures that correspond to different stages of the combustion process. It was shown that the crystalline structure developed gradually, first with crystallization of nano-sized NiO particles (400°–700°C), which was followed by crystallization of YSZ (800°–900°C). The final composite material after heat treatment at 1100°C comprised of nano-crystals with an average size of 6.5±2 nm.     

Influence of near-wall modelling on boiling flow simulation

The capability of the three-dimensional two-fluid codes to simulate the local boiling flow processes has been assessed. Boiling flow experiments of Roy et al. [Roy, R.P., Kang, S., Zarate, J.A., Laporta, A., 2002. Turbulent subcooled boiling flow—experiments and simulations, J. Heat Transfer 124, 73-93] and Lee et al. [Lee, T.H., Park, G.C., Lee, D.J., 2002. Local flow characteristics of subcooled boiling flow of water in a vertical concentric annulus. Int. J. Multiphase Flow 28, 1351-1368], both performed in annular vertical channels were used as an experimental benchmark data set. The boiling flow is strongly affected by local mechanisms in the boundary layer near the heated wall. In this paper, the influence of near-wall modelling on the distribution of flow parameters at flow boiling has been analyzed. A generic wall function model for 3D two-fluid codes, based on surface roughness analogy has been proposed instead of commonly used single-phase log-law model. The new model has been implemented in the code CFX-4.4. In general, better agreement of phase velocities with experimental data were obtained with the new model. Presented results show that the influence of nucleating bubbles on the near-wall velocity profile should be taken into account. The second goal of this paper is to compare the NEPTUNE_CFD simulations against CFX-4.4 results and experimental data.     

Direct contact condensation induced transition from stratified to slug flow

Selected condensation-induced water hammer experiments performed on PMK-2 device were numerically modelled with three-dimensional two-fluid models of computer codes NEPTUNE_CFD and CFX. Experimental setup consists of the horizontal pipe filled with the hot steam that is being slowly flooded with cold water. In most of the experimental cases, slow flooding of the pipe was abruptly interrupted by a strong slugging and water hammer, while in the selected experimental runs performed at higher initial pressures and temperatures that are analysed in the present work, the transition from the stratified into the slug flow was not accompanied by the water hammer pressure peak. That makes these cases more suitable tests for evaluation of the various condensation models in the horizontally stratified flows and puts them in the range of the available CFD (Computational Fluid Dynamics) codes. The key models for successful simulation appear to be the condensation model of the hot vapour on the cold liquid and the interfacial momentum transfer model. The surface renewal types of condensation correlations, developed for condensation in the stratified flows, were used in the simulations and were applied also in the regions of the slug flow. The “large interface” model for inter-phase momentum transfer model was compared to the bubble drag model. The CFD simulations quantitatively captured the main phenomena of the experiments, while the stochastic nature of the particular condensation-induced water hammer experiments did not allow detailed prediction of the time and position of the slug formation in the pipe. We have clearly shown that even the selected experiments without water hammer present a tough test for the applied CFD codes, while modelling of the water hammer pressure peaks in two-phase flow, being a strongly compressible flow phenomena, is beyond the capability of the current CFD codes.     

Wollastonite‐reinforced polypropylene composites modified with novel metallocene EPR copolymers. II. Mechanical properties and adhesion

Mechanical properties and adhesion phenomena of isotactic polypropylene/wollastonite/metallocene propylene‐ethylene copolymers (iPP/W/EPR) composites were studied as a function of metallocene propylene‐based copolymers content from 0 to 20 vol%. The composites with different surface treated wollastonites and two types of EPR have shown similar behavior of most mechanical properties except elongation at break and impact strength respective of the difference in some characteristics of used EPR elastomers. The increase and the difference in elongation at break could be explained by renewed spherulitic morphology of the iPP matrix. Stronger interactions between EPR‐1 and two used types of wollastonites than between EPR‐2 and corresponding wollastonites concluded from the surface properties led to the difference in impact strength behavior. The determined mechanical properties confirm the assumption coming out of structural investigations that metallocene EPR elastomers are rather efficient impact modifiers than encapsulation compatibilizers for the iPP/wollastonite composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Simulation of Fuzzy-Logic-Based Intelligent Wheelchair Control System

Fuzzy logic control system for an intelligent wheelchair aimed for assistance by the severely handicapped persons is presented in the paper. It is based on a computer simulation of wheelchair navigation, in which fuzzy logic enables control priority to smoothly alternate between manual and automatic control of the wheelchair in the vicinity of obstacles. The main purpose of designing and simulating this control approach is to improve the safety of a wheelchair in the presence of obstacles. To analyze the success of the wheelchair control, a dynamic model of the wheelchair, together with the models of distance sensors, has been developed using Lagrange analysis.     

Efficient modeling of polysaccharide conformations based on Small-Angle X-ray Scattering experimental data

Small-Angle X-ray Scattering (SAXS) curves of pullulan oligomers and gellan gum were modeled with a new string of beads model. The model enables one to simulate polysaccharide single helices with different pitch values, number of monomers per pitch, and cross-sectional radius, as well as different random coils with excluded volume taken into account. The vast conformational space of possible polysaccharide structures is systematically scanned and, for each selected polysaccharide 3D structure, the SAXS curve is calculated and compared to the SAXS experimental data. All structures with RMSSD ≤ 1 are retained as the solutions. By allowing the distribution of equally good solutions to the given experimental SAXS curve, the new model enables one to get a phase space of possible polymer structures in the aqueous environment. Most importantly it avoids using pre-assumed secondary structure elements to fit the experimental data.     

Part I: the influence of serial repitching of Saccharomyces pastorianus on the uptake dynamics of metal ions and fermentable carbohydrates during the fermentation of barley and gluten‐free buckwheat and quinoa wort

Recently, research has been focusing on the use of alternative raw materials for brewing purposes and gluten‐free beer‐like beverages from malted buckwheat and quinoa are of commercial interest. A common commercial process involves the serial repitching of the yeast biomass, but this has not been described using buckwheat and quinoa wort fermentations. Our research studies (Parts I–III) explored the serial repitching of the yeast strain Saccharomyces pastorianus TUM 34/70 on the composition of a barley, buckwheat and quinoa fermentation medium. The present paper focuses on the fermentation performance and the uptake dynamics of metal ions and fermentable carbohydrates. Both pseudocereals showed high variations in all of the attributes examined during successive fermentations. In buckwheat the differences between successive fermentations were similar to those observed with barley, whereas differences in quinoa varied quite significantly from those observed with barley and showed a directional trend, suggesting a general weakening of the yeast from the sixth successive fermentation onward. In particular, the assimilation of the fermentable carbohydrates lessened and metal ion uptake appeared poorly controlled. It was concluded that buckwheat showed good potential for serial repitching of S. pastorianus TUM 34/70, whereas serial repitching of a quinoa wort appeared to be limited to five or six fermentations. Copyright © 2015 The Institute of Brewing & Distilling     

Two-layer synchronized ternary quantum-dot cellular automata wire crossings

ABSTRACT: : Quantum-dot cellular automata are an interesting nanoscale computing paradigm. The introduction of the ternary quantum-dot cell enabled ternary computing, and with the recent development of a ternary functionally complete set of elementary logic primitives and the ternary memorizing cell design of complex processing structures is becoming feasible. The specific nature of the ternary quantum-dot cell makes wire crossings one of the most problematic areas of ternary quantum-dot cellular automata circuit design. We hereby present a two-layer wire crossing that uses a specific clocking scheme, which ensures the crossed wires have the same effective delay.