Effects of alumina on the crystallization behavior, densification and dielectric properties of BaO–ZnO–SrO–CaO–Nd2O3–TiO2–B2O3–SiO2 glass–ceramics

The alumina addition effects on the crystallization, sintering behaviors and dielectric properties of BaO–ZnO–SrO–CaO–Nd₂O₃–TiO₂–B₂O₃–SiO₂ (Ba–Zn–Sr–Ca–Nd–Ti–B–Si) glass powder were investigated using the differential thermal analyzer (DTA), thermo-mechanical analyzer (TMA), X-ray diffractometer (XRD). The results showed that the addition of alumina powder into Ba–Zn–Sr–Ca–Nd–Ti–B–Si glass changed the crystallization sequence from Nd₂Ti₄O₁₁–Nd_0.66TiO₃ to Nd₂Ti₃O_8.7–Nd₂Ti₂O₇–Nd₂Ti₄O₁₁and increased the densification activation energy due to the dissolution of Al³⁺ ions into the glass structure. Fully densified 30 vol.% alumina-added Ba–Zn–Sr–Ca–Nd–Ti–B–Si glass can be obtained via glass viscous flow before the second and third crystalline phases, Nd₂Ti₂O₇ and Nd₂Ti₄O₁₁crystallization. The 30 vol.% alumina-added Ba–Zn–Sr–Ca–Nd–Ti–B–Si glass–ceramics sintered at 900 °C exhibited a high dielectric constant of 17 and a quality factor of about 820, which provided a promising candidate for LTCC applications.     

Phase evolution and thermal behaviors of the solid-state reaction between SrCO3 and Al2O3 to form SrAl2O4 under air and CO2-air atmospheres

The solid-state reactions between SrCO₃ and Al₂O₃ forming SrAl₂O₄ under air and CO₂-air atmospheres were investigated. The solid-state reaction between SrCO₃ and Al₂O₃ under a CO₂ atmosphere can be separated into multiple reaction stages. The first stage is attributed to the formation of SrAl₂O₄ resulting from the reaction between SrCO₃ and Al₂O₃. The diffusion of Al₂O₃ through the product layer then takes place to continue the reaction. At a higher temperature, the Sr₃Al₂O₆ formation reaction occurs due to the chemical reaction between SrCO₃ and SrAl₂O₄. The SrCO₃ is thermally finally decomposed. The resulting SrO may diffuse rapidly through the product layer, producing pure SrAl₂O₄ formation via a complicated diffusion process at a much higher temperature. These reaction stages occur at very close temperatures under an air atmosphere, leading to a complex reaction between the solids in air.     

Functional monomers and polymers, 116. Asymmetric addition of n-butyllithium to aldehydes by chiral polymers and related compounds containing dimethylamino bornanol moieties

Asymmetric addition reaction of n-butyllithium to aldehydes was studied by using chiral polystyrene derivatives and chiral low molecular model compounds, both of which were derived from cis,endo-3-dimethylamino-2-hydroxybornane. The higher optical yields were achieved by using low molecular model compounds, and particularly the highest value was obtained in the case when ether was used as the solvent. The effect of reaction temperature, sort of the solvents and the molar ratio of the reagent to aldehyde on the asymmetric addition was also discussed.     

Human-centred approaches in slipperiness measurement.

A number of human-centred methodologies--subjective, objective, and combined--are used for slipperiness measurement. They comprise a variety of approaches from biomechanically-oriented experiments to psychophysical tests and subjective evaluations. The objective of this paper is to review some of the research done in the field, including such topics as awareness and perception of slipperiness, postural and balance control, rating scales for balance, adaptation to slippery conditions, measurement of unexpected movements, kinematics of slipping, and protective movements during falling. The role of human factors in slips and falls will be discussed. Strengths and weaknesses of human-centred approaches in relation to mechanical slip test methodologies are considered. Current friction-based criteria and thresholds for walking without slipping are reviewed for a number of work tasks. These include activities such as walking on a level or an inclined surface, running, stopping and jumping, as well as stair ascent and descent, manual exertion (pushing and pulling, load carrying, lifting) and particular concerns of the elderly and mobility disabled persons. Some future directions for slipperiness measurement and research in the field of slips and falls are outlined. Human-centred approaches for slipperiness measurement do have many applications. First, they are utilized to develop research hypotheses and models to predict workplace risks caused by slipping. Second, they are important alternatives to apparatus-based friction measurements and are used to validate such methodologies. Third, they are used as practical tools for evaluating and monitoring slip resistance properties of footwear, anti-skid devices and floor surfaces.