Chemical Synthesis,Sintering and Piezoelectric Properties of Ba0.85Ca0.15 Zr0.1Ti0.9O3 Lead‐Free Ceramics

The preparation of Ba_0.85Ca_0.15 Zr_0.1Ti_0.9O₃ (BCZT) powders by wet chemical methods has been investigated, and the powders used to explore relationships between the microstructure and piezoelectric properties (d₃₃ coefficient) of sintered BCZT ceramics. Sol–gel synthesis has been shown to be a successful method for the preparation of BCZT nanopowders with a pure tetragonal perovskite phase structure, specific surface area up to 21.8 m²/g and a mean particle size of 48 nm. These powders were suitable for the fabrication of dense BCZT ceramics with fine‐grain microstructures. The ceramics with the highest density of 95% theoretical density (TD) and grain size of 1.3 μm were prepared by uniaxial pressing followed by a two‐step sintering approach which contributed to the refinement of the BCTZ microstructure. A decrease in the grain size to 0.8–0.9 μm was achieved when samples were prepared using cold isostatic pressing. Using various sintering schedules, BCZT ceramics with broad range of grain sizes (0.8–60.5 μm) were prepared. The highest d₃₃ = 410.8 ± 13.2 pC/N was exhibited by ceramics prepared from sol–gel powder sintered at 1425°C, with the relative density of 89.6%TD and grain size of 36 μm.     

Cross-linked poly(ethylene vinyl acetate) (EVA)/low density polyethylene (LDPE)/metal hydroxides composites for wire and cable applications

Formulations of chemically cross-linked poly(ethylene vinyl acetate) (EVA) and low density polyethylene (LDPE) blends containing metal hydroxides flame retardants such as aluminum hydroxide (ATH) and magnesium hydroxide (MH) were prepared. Comparison of both type of metal hydroxides in respect of their influence on flammability as well as mechanical, thermal, and electrical properties of EVA/LDPE composites is presented. Most of the investigated properties are better for composites containing MH in comparison with composites containing ATH. Influence of various EVA/LDPE ratios on investigated properties is presented as well. Importance of improving compatibility using compatibilizers to improve some of the investigated properties is described. Polyethylene grafted with maleic anhydride (PEgMA) was found to be better compatibilizer for ATH than vinyl silanes.     

Is sedation-induced BOLD fMRI low-frequency fluctuation increase mediated by increased motion?

Object

Increases in low-frequency fluctuations (LFF, 0.01–0.1 Hz) of BOLD fMRI signal were observed during sedation and sleep. We tested the hypothesis that sedation-induced LFF increases may be mediated by increased head motion likely associated with these brain states.

Materials and Methods

Twenty healthy volunteers were scanned in resting-state baseline and (15 thereof) in midazolam sedation condition. After standard preprocessing, LFF power was computed from average time series from 14 ROIs representing 5 functional networks (visual, motor, auditory, default mode, dorsal attentional). We assessed the effects of sedation on LFF and indirect effects of head motion (mean relative displacement) using mediation analysis.

Results

Sedation increased LFF power with the indirect effect of motion on sedation-induced LFF significant for all networks. Global mean corrected data showed similar but weaker results: significant total effect for auditory, motor and visual; significant mediation for auditory and motor networks. Motion was strongly correlated with LFF even at baseline. Reported results were significant at p < 0.05.

Conclusion

The study confirms that conscious sedation induces LFF increase, but demonstrates that this effect is mediated by increased head motion. Hence, caution in design and interpretation is recommended for studies comparing subjects or conditions differently predisposing to head motion.     

The carbonization of thin polyaniline films

Polyaniline films on silicon and ceramic supports were prepared in situ during the oxidative polymerization of aniline. The films were heated up to 500 °C in an inert nitrogen atmosphere. The changes in molecular structure during the carbonization have been studied by infrared spectroscopy and Raman scattering using 514, 633 and 785 nm laser excitation lines. The transformation from polyaniline salt to the base form has been detected above 100 °C. The conversion to nitrogen-containing carbon-like material followed above 200 °C. The molecular structure of the films produced during heating to 500 °C contains crosslinked phenazine-like and oxidized quinonoid units. The aniline oligomers deposited on the support in the early stages of aniline oxidation are stable during heating as it has been observed by resonance Raman scattering using 785 nm laser excitation line. The water contact angles changed after carbonization, and the films became more hydrophilic as carbonization progressed.     

Polymer films releasing nisin and/or natamycin from polyvinyldichloride lacquer coating: Nisin and natamycin migration,efficiency in cheese packaging

Polyethylene films coated by commercially available polyvinyldichloride (PVdC) as well as nitrocellulose (NC) lacquer with addition of natamycin preparation Delvocid® (16.7% w/w of natamycin in lacquer) were studied at 6 and 23 °C to determine the preservative migration into distilled water. The films released natamycin at maximal level 2.34 ± 0.32 mg/dm². The diffusion coefficient of 0.79 × 10⁻¹⁰ ± 0.29 × 10⁻¹⁰ cm²/s and 1.03 × 10⁻¹⁰ ± 0.17 × 10⁻¹⁰ cm²/s was determined for natamycin transport in PVdC lacquer layer at 6 and 23 °C, respectively. For nitrocellulose lacquer the diffusion coefficient of 0.89 × 10⁻¹⁰ ± 0.16 × 10⁻¹⁰ cm²/s was found at 23 °C. The coextruded polyamide/polyethylene film coated with the PVdC lacquer containing both nisin (16.7% w/w of preparation Nisaplin®) and natamycin (see above) provided inhibitory effect against selected indicator microorganisms (Penicillium expansum, Fusarium culmorum, Lactobacillus helveticus, Listeria ivanovií). This film was unsuitable for the packaging of the surface ripened cheese Olomoucké tvar??ky. On the other hand, it was able to prevent the growth of spoilage microorganisms on the surface of the packaged soft cheese Bla?ácké zlato.     

Thermodynamics of the liquid Co-Cu system and calculation of phase diagram

Knudsen-cell mass spectrometric measurements have been carried out in the liquid phase of the Co-Cu system in the concentration range 25.0 to 85.9 at. % Cu in the temperature range 1347 to 1587 °C. The molar excess Gibbs energy, enthalpy and entropy of mixing, as well as the thermodynamic activities of components in the liquid Co-Cu system were determined using the composition and temperature dependence of the ratio of intensities of ⁵⁹Co and ⁶³Cu ions. The results show that a subregular solution model would fit measured data well (2-parameter thermodynamically adapted power (TAP) series: C _n ^H in J·mol⁻¹; C ₁ ^H =35,961, C ₂ ^H =−5573.2; C _n ^S in J·mol^−1·K−1; C ₁ ^S =5.54, C ₂ ^S =−3.35). A special experiment verified solid-liquid phase equilibrium at 1327 °C and the phase diagram was calculated.     

Surface and porous recast layer analysis in µ-EDM of MWCNT-Al2O3 composites

Machining of ceramic materials has been a major challenge owing to high hardness and brittleness. The reinforcement of a conducting filler allows permissible machining in electrical discharge machining (EDM) process. The current effort analyses the impact of multi-walled carbon nanotubes (MWCNT) of concentrations of 2.5 and 5 vol. %, as conducting filler towards machinability of alumina composites in µ-EDM process. The influence of tool materials and its rotation are closely analyzed. A successful machining process is observed in both the two composites, with a higher material removal rate (MRR) in 5 vol. % MWCNTs. When the tool starts to rotate at 750 rpm, an increment of around 60–65% is observed in MRR for both the two composites. Similarly, the surface roughness (R_a) decreases by a factor of 20?25%. The brass tool is observed to yield better machining capabilities due to the frequent initiation of sparks. A highly porous machined surface is observed in both the two composites. This scenario depicts the spalling effect as more dominant than melting-evaporation effect. The extent of porous recast layer on the drilled edges is found to reduce with increasing the speed of tool rotation.     

Particle swarm optimization for problems with variable number of dimensions

Some real-life optimization problems, apart from dependence on the combination of state variables, also show dependence on the complexity of the model describing the problem. Changing model complexity implies changing the number of decision space dimensions.

A new method called Particle Swarm Optimization for Variable Number of Dimensions is developed here. The well-known particle swarm optimization procedure is modified to handle spaces with a variable number of dimensions within a single run. Some well-known benchmark problems are modified to depend on the number of dimensions. Novel performance metrics are defined in the article to evaluate convergence properties of the method. Some recommendations for setting the optimization are made according to results of the method on the proposed benchmark test suite. The method is compared with conventional swarm strategies able to solve problems with variable number of dimensions.     

Updated energy policy of the Czech Republic may result in instability of the electricity grid in Central Europe

Brown coal is the resource used for generating half of the electricity and most of the heat that is distributed over the public network in the Czech Republic, which is one of the largest exporters of electricity in Europe. As a result of public call for cleaner energy sources, the energy policy of the Czech Republic has been updated recently. The government act calls for significant decrease in brown coal mining. Prediction of material flow analysis for the entire energy sector of the Czech Republic till 2040 was carried out. The data revealed mounting evidence indicating that the novel energy policy proposed was too ambitious which may affect the stability of the power grid in the surrounding countries. Worse still, it appears that after 2025, the Czech energy sector will be in short supply of limestone, which is likely to result in lower levels of flue gas desulphurization or limestone mining in protected landscape areas. It is concluded that further diversification of local energy resources is advisable to avoid unwanted negative environmental impacts.     

Reference governor for constrained piecewise affine systems

We present a methodology for designing reference tracking controllers for constrained, discrete-time piecewise affine systems. The approach follows the idea of reference governor techniques where the desired set-point is filtered by a system called the “reference governor”. Based on the system current state, set-point, and prescribed constraints, the reference governor computes a new set-point for a low-level controller so that the state and input constraints are satisfied and convergence to the original set-point is guaranteed.In this note we show how to design a reference governor for constrained piecewise affine systems by using polyhedral invariant sets, reachable sets, multiparametric programming and dynamic programming techniques.