Positron Annihilation Study of Zirconia Nanopowders and Nanoceramics Stabilized by Magnesia and Ceria

Positron lifetime (LT) and coincidence Doppler broadening (CDB) measurements on nanopowders and ceramics of ceria‐ and magnesia‐stabilized zirconia (CeSZ and MgSZ, respectively) are presented. The nanopowders were prepared by the coprecipitation technique. Effects of nanopowder calcination and sintering at various temperatures were investigated. In the nanopowders, the two kinds of open‐volume defects associated with grain boundaries (GBs) could be identified via positron trapping: (i) vacancy‐like misfit defects situated along GBs and (ii) larger defects at the intersections of at least three GBs (triple points). CDB measurements on CeSZ compacted nanopowders indicated a segregation of Ce ions along GBs. A few percent fractions of positrons were found to form positronium localized in pores of ≈1.8 nm diameter in compacted nanopowders. Sintering of nanopowders at 1500°C appeared to be sufficient for disappearance of pores and triple point defects. In sintered ceramics, contrary to compacted nanopowders, positrons were trapped in zirconium vacancies in grain interiors.     

Hormonal Regulation and Crosstalk of Auxin/Cytokinin Signaling Pathways in Potatoes In Vitro and in Relation to Vegetation or Tuberization Stages

Auxins and cytokinins create versatile regulatory network controlling virtually all aspects of plant growth and development. These hormonal systems act in close contact, synergistically or antagonistically, determining plant phenotype, resistance and productivity. However, the current knowledge about molecular interactions of these systems is still scarce. Our study with potato plants aimed at deciphering potential interactions between auxin and cytokinin signaling pathways at the level of respective gene expression. Potato plants grown on sterile medium with 1.5% (vegetation) or 5% (tuberization) sucrose were treated for 1 h with auxin or cytokinin. Effects of these two hormones on expression profiles of genes belonging to main signaling pathways of auxin and cytokinin were quantified by RT-qPCR. As a result, several signaling genes were found to respond to auxin and/or cytokinin by up- or down-regulation. The observed effects were largely organ-specific and depended on sucrose content. Auxin strongly reduced cytokinin perception apparatus while reciprocal cytokinin effect was ambiguous and sucrose-dependent. In many cases, functional clustering of genes of the same family was observed. Promoters in some clusters are enriched with canonic hormone-response cis-elements supporting their direct sensitivity to hormones. Collectively, our data shed new light on the crosstalk between auxin- and cytokinin signaling pathways.     

Changes of liquid-crystalline polymer structure with temperature

Summary Thermal changes in the structural state of liquid crystalline polymers with mesogenic side groups and the kinetics of mesophase formation were studied by means of smallangle X-ray scattering.Part 3: V.Tsulcruk,O.Lokhonya,V.Shilov,V.Kuzmina,Yu.Lipatov Makromol.Chem,,Rapid Commun.4,595(1983)     

Elastic scattering and light transport in three-dimensional collagen gel constructs: a mathematical model and computer simulation approach

A mathematical modeling approach for elastic scattering and light propagation is presented, which can be used to obtain the scattering coefficient, the index of refraction, and the distribution of the collagen fibrils in a gel. Collagen fibrils can be realistically represented by small cylindrical particles. The analysis of the scattering of light by such particles provides the scattering coefficient. Light transport in multilayered tissues has been modeled and the collagen fibrils scattering coefficient has been considered as main input parameters. Assuming that a gel is composed of fibrils with the same diameter, it is possible to obtain all the input parameters of the model and, therefore, a simulated spectrum. This can be repeated for several diameters. Considering a gel composed of fibrils with different diameters, it is possible to obtain a best-fitting simulated spectrum as a weighted sum (least-square-error based) of the spectra corresponding to several fibril diameters, and, therefore, obtain an estimate of the percentages of fibrils of each diameter in the gel. Moreover, the scattering coefficient and refractive index, which are also provided by the model, are relevant parameters as they relate to tissue properties in their own right.     

Antecedents and consequences of trust in a social media brand: A cross-cultural study of Twitter

This study extends brand relationship theory to the context of the microblogging platform Twitter. The authors investigate the impact of Twitter trust on users’ intentions to continue using the platform and to “follow” brands that are hosted on Twitter (the trust transfer phenomenon). They also explore the role of perceived self-Twitter personality match in strengthening trust towards the Twitter brand. A cross-cultural American–Ukrainian sample allows to identify potential culture-based differences in brand personality and brand trust concepts. The results show that the positive effect of trust in Twitter on its users’ patronage intentions is robust across two cultures with diverse history and ideology. An important novel finding is the influence of trust in Twitter on patronage intentions towards the businesses hosted on Twitter. However, this relationship reaches statistical significance only in the Ukrainian sample, signaling potential differences in the trust transfer processes in different cultures. The study confirms the role of similarity in personality traits between Twitter users and the Twitter brand in engendering trust in Twitter. The salience of different personality traits in the “personality match – Twitter trust” link for different cultures suggests important implications for global marketers.     

Microstructural parameters of dispersion strengthened Cu–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> materials

The aim of the article was to evaluate the microstructural parameters of Cu–Al₂O₃ dispersion strengthened materials with different volume fraction of Al₂O₃ phase. For analyses of dispersoids Al₂O₃, the extraction carbon replica was used. The distribution of Al₂O₃ particles in the matrix was estimated by three methods (quadrant count method, polygonal method, and by interparticle distances), these methods showed that particle distribution in material with 1 vol.% of Al₂O₃ is very close to the Poisson point process (PPP), which is a model of randomly distributed points. Particle distributions in materials with 8 and 10 vol.% of Al₂O₃ achieve features of regularity proved mainly by the spherical contact distance.     

Metformin Attenuates Postinfarction Myocardial Fibrosis and Inflammation in Mice

Diabetes is a major risk factor for the development of cardiovascular disease with a higher incidence of myocardial infarction. This study explores the role of metformin, a first-line antihyperglycemic agent, in postinfarction fibrotic and inflammatory remodeling in mice. Three-month-old C57BI/6J mice were submitted to 30 min cardiac ischemia followed by reperfusion for 14 days. Intraperitoneal treatment with metformin (5 mg/kg) was initiated 15 min after the onset of reperfusion and maintained for 14 days. Real-time PCR was used to determine the levels of COL3A1, αSMA, CD68, TNF-α and IL-6. Increased collagen deposition and infiltration of macrophages in heart tissues are associated with upregulation of the inflammation-associated genes in mice after 14 days of reperfusion. Metformin treatment markedly reduced postinfarction fibrotic remodeling and CD68-positive cell population in mice. Moreover, metformin resulted in reduced expression of COL3A1, αSMA and CD68 after 14 days of reperfusion. Taken together, these results open new perspectives for the use of metformin as a drug that counteracts adverse myocardial fibroticand inflammatory remodeling after MI.     

The mechanism of the failure of the dispersion-strengthened Cu–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanosystem

The method of “in situ tensile testing in SEM” is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thank to which the initiation and development of plastic deformation and fracture can be reliably described. The deformation and fracture mechanisms of Cu–Al₂O₃ nanomaterials with 5 vol.% of Al₂O₃ phase has been analyzed using technique of the “in situ tensile testing in SEM.” It has been shown that the deformation process causes break-up of large Al₂O₃ particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations, a model of damage and/or fracture mechanisms has been proposed.