Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Sodium deficiency in Na0.5Bi0.5TiO3

Abstract: The mechanism of solid-state synthesis for Na0.5Bi0.5TiO3 was investigated using X-ray powder diffraction, scanning electron microscopy and wavelength-dispersive X-ray spectroscopy. The results showed that a Na0.5−xBi0.5TiO3−x/2 homogeneity region, with Na0.5Bi0.5TiO3 and Na0.47Bi0.5TiO3−δ as the end-members (0 ≤ x ≤ 0.03), exists in the Na2O–Bi2O3–TiO2 system. The formation of any member from the homogeneity region starts with the formation of the deficient end-member, i.e., Na0.47Bi0.5TiO3−δ. However, the reaction continues toward a nominal composition when a sufficiently high temperature and/or a long firing time are used. The conversion of the latter reaction may be followed by the observation of the crystal symmetry, which changes from the cubic-like toward the rhombohedral as the reaction proceeds from Na0.47Bi0.5TiO3−δ to Na0.5Bi0.5TiO3. Differences in the dielectric, ferroelectric and piezoelectric properties were observed for the samples from the homogeneity region, and these can be related to the stoichiometry variation along the homogeneity region and thus to the variation in the vacancy concentration. The most striking difference is the change in the piezoelectric constant d33, which increases from 82 pC N−1 to 97 pC N−1 as the composition of the ceramics changes from Na0.5Bi0.5TiO3 to Na0.47Bi0.5TiO3−δ.

Validation of the Fiala multi-node thermophysiological model for UTCI application

Abstract: The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index (UTCI) was its capability of accurate simulation of human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing the temporal variation of outdoor conditions. In the first part of this study, available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over a wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response, as shown by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was subjected to extensive validation using the results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-mean-square deviations of 1.35 ± 1.00°C and 0.32 ± 0.20°C, respectively.