Ferroelectric properties of composites containing BaTiO3 nanoparticles of various sizes.

Size effects, including the occurrence of superparaelectric phases associated with small scale, are a significant research topic for ferroelectrics. Relevant phenomena have been explored in detail, e.g. for homogeneous, thin ferroelectric films, but the related effects associated with nanoparticles are usually only inferred from their structural properties. In contrast, this paper describes all the steps and concepts necessary for the direct characterization and quantitative assessment of the ferroelectric properties of as-synthesized and as-received nanoparticles. The method adopted uses electrical polarization measurements on polymer matrix composites containing ferroelectric nanoparticles. It is applied to ten different BaTiO3 particle types covering a size range from 10 nm to 0.8 µm. The influence of variations of particle characteristics such as tetragonality and dielectric constant is considered based on measurements of these properties. For composites containing different particle types a clearly differing polarization behaviour is found. For decreasing particle size, increasing electric field is required to achieve a given level of polarization. The size dependence of a measure related to the coercive field revealed by this work is qualitatively in line with the state of the knowledge for ferroelectrics having small dimensions. For the first time, such results and size effects are described based on data from experiments on collections of actual nanoparticles.

Structural correlate of atrial fibrillation in human patients.

OBJECTIVE: We tested the hypothesis that structural remodeling of cellular connections, alterations in the expression of connexins (Cx), and an increase in fibrosis represent anatomic substrates of atrial fibrillation (AF). METHODS: In 31 patients with AF undergoing a Maze procedure and 22 patients in sinus rhythm (SR), biopsies were taken intraoperatively from the right atrial (RA) free wall and appendages and investigated with immunoconfocal and electron microscopy. RESULTS: All patients with AF exhibited a concomitant lateralization of gap junctional proteins Cx43 and Cx40, and N-cadherin (the major mechanical junction protein), instead of being confined to the intercalated discs, as observed in SR. These results were confirmed by quantitative immunoconfocal analysis and electron microscopy. Among diverse junctional proteins, in AF, Cx40 was markedly heterogeneous in distribution. As compared with the SR group, Cx43 was significantly decreased in AF by 57% in RA appendages and by 56% in RA free wall. Cx40 was reduced by 54% in appendages, but had a tendency to be increased in the RA free wall. Collagen I was significantly higher in AF than in SR by 48% in RA appendages and by 69% in the RA free wall tissues. CONCLUSIONS: The structural correlate of AF comprises extensive concomitant remodeling of mechanical and electrical junctions, reduction of Cx43, heterogeneous distribution of Cx40 in terms of different amounts of Cx40 in different RA tissues or in spatially adjacent regions of atrial myocardium. These changes, together with augmentation of fibrosis, may underlie localized conduction abnormalities and contribute to initiation and self-perpetuation of re-entry pathways and AF.