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Sosnowiec, Poland

Datta K.,University of Warwick | Thomas P.A.,University of Warwick | Roleder K.,Silesian University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Temperature-dependent structural phase transitions and dielectric properties for a series of x Na0.5 Bi0.5 TiO3 - (1-x) BaTiO3 (NBT-BT) samples where x ranges from 0.05 to 0.30 have been investigated. Non-ambient x-ray diffraction together with dielectric data as a function of temperature have demonstrated an enhancement in the ferroelectric to paraelectric phase transition temperature with the increase in NBT content, including inhibition of two well-known low-temperature polymorphic phase transitions of BaTiO3. Anomalous dielectric response has been observed for samples with x≥0.20 suggesting a crossover from a first-order to a second-order phase transition. The critical point lies between x=0.15 and x=0.20. Deviation from the classical Curie-Weiss law has been seen for samples having x≥0.10. A modified Curie-Weiss law was employed to model the dielectric response in the paraelectric phase and the maximum value of the critical exponent γ was found to be 1.45 for x=0.30. It is suggested that the dielectric properties are heavily influenced by the induced strain upon doping rather than chemical inhomogeneities and structural disorder, which are common occurrences in doped ferroelectrics. © 2010 The American Physical Society.

The process of ciliogenesis that accompanies the differentiation of the thyroid gland in grass snake Natrix natrix L. embryos was studied ultrastructurally. Based on this study, it can be concluded that the ciliogenesis occurred in two waves and that new centrioles duplicated via centriolar pathways. The first wave of ciliogenesis started in the post-mitotic thyrocytes before their polarisation. It ended approximately halfway through the developmental period. The second wave of ciliogenesis took place after the polarization of thyrocytes and before the resting phase of the embryonic thyroid. This wave of ciliogenesis stopped shortly before hatching when fully differentiated thyrocytes restarted their activity. During the first half of thyroid differentiation, the cilia were formed "intracellularly" but during the second half, they differentiated "extracellularly" In the differentiating thyrocytes one cilium per cell was found; however, it could not be excluded that more than one cilium per cell may be formed. These cilia lacked central fibres and therefore they had a 9. +. 0 formula that suggested that they were immotile. © 2012 Elsevier Ltd.

Zawisza B.,Silesian University
Journal of Analytical Atomic Spectrometry | Year: 2010

The extremely low fluorescent yield and long-wavelength characteristic radiation are the major limitations for direct XRF determination of the elements of low atomic numbers. In the case of lithium, the determination of this element by X-ray fluorescence spectrometry (XRF) is not possible. Thus, an indirect method for the determination of lithium by X-ray fluorescence spectrometry was proposed. The method is based on the determination of lithium through iron in the potassium lithium periodatoferrate(III) complex. The complex was collected on the membrane filter and the Fe Kα line was measured by XRF. The optimum conditions for LiKFeIO6 complex formation and XRF measurement were studied. A good ratio of lithium to iron (1 to 8) and a sensitive Fe Kα line give the possibility to determine a low lithium amount. The proposed method allows the determination of 20 g of lithium collected on a filter. The validity of the proposed method was verified with certified lithium ores. The agreement between XRF analysis and certified values is satisfactory and indicates the usefulness of the carried out method. © The Royal Society of Chemistry 2010.

Racki G.,Silesian University
Acta Palaeontologica Polonica | Year: 2012

For the past three decades, the Alvarez impact theory of mass extinction, causally related to catastrophic meteorite impacts, has been recurrently applied to multiple extinction boundaries. However, these multidisciplinary research efforts across the globe have been largely unsuccessful to date, with one outstanding exception: the Cretaceous-Paleogene boundary. The unicausal impact scenario as a leading explanation, when applied to the complex fossil record, has resulted in force-fitting of data and interpretations ("great expectations syndrome". The misunderstandings can be grouped at three successive levels of the testing process, and involve the unreflective application of the impact paradigm: (i) factual misidentification, i.e., an erroneous or indefinite recognition of the extraterrestrial record in sedimentological, physical and geochemical contexts, (ii) correlative misinterpretation of the adequately documented impact signals due to their incorrect dating, and (iii) causal overestimation when the proved impact characteristics are doubtful as a sufficient trigger of a contemporaneous global cosmic catastrophe. Examples of uncritical belief in the simple cause-effect scenario for the Frasnian-Famennian, Permian-Triassic, and Triassic-Jurassic (and the Eifelian-Givetian and Paleocene-Eocene as well) global events include mostly item-1 pitfalls (factual misidentification), with Ir enrichments and shocked minerals frequently misidentified. Therefore, these mass extinctions are still at the first test level, and only the F-F extinction is potentially seen in the context of item-2, the interpretative step, because of the possible causative link with the Siljan Ring crater (53 km in diameter). The erratically recognized cratering signature is often marked by large timing and size uncertainties, and item-3, the advanced causal inference, is in fact limited to clustered impacts that clearly predate major mass extinctions. The multi-impact lag-time pattern is particularly clear in the Late Triassic, when the largest (100 km diameter) Manicouagan crater was possibly concurrent with the end-Carnian extinction (or with the late Norian tetrapod turnover on an alternative time scale). The relatively small crater sizes and cratonic (crystalline rock basement) setting of these two craters further suggest the strongly insufficient extraterrestrial trigger of worldwide environmental traumas. However, to discuss the kill potential of impact events in a more robust fashion, their location and timing, vulnerability factors, especially target geology and palaeogeography in the context of associated climate-active volatile fluxes, should to be rigorously assessed. The current lack of conclusive impact evidence synchronous with most mass extinctions may still be somewhat misleading due to the predicted large set of undiscovered craters, particularly in light of the obscured record of oceanic impact events. Copyright © 2012.

The differentiation of the thyroid primordium of reptilian species is poorly understood. The present study reports on structural and ultrastructural studies of the developing thyroid gland in embryos of the grass snake Natrix natrix L. At the time of oviposition, the thyroid primordium occupied its final position in the embryos. Throughout developmental stages I-IV, the undifferentiated thyroid primordium contained cellular cords, and the plasma membranes of adjacent cells formed junctional complexes. Subsequently, the first follicular lumens started to form. The follicular lumens were of intracellular origin, as in other vertebrate species, but the mechanism of their formation is as yet unclear. At developmental stages V-VI, the thyroid anlage was composed of small follicles with lumens and cellular cords. Cells of the thyroid primordium divided, and follicles were filled with a granular substance. At developmental stage VI, the cells surrounding the follicular lumen were polarized, the apical cytoplasm contained dark granules and the Golgi complex and the rough endoplasmic reticulum (RER) developed gradually. Resorption of the colloid began at developmental stage VIII. At the end of this stage, the embryonic thyroid gland was surrounded by a definitive capsule. During developmental stages IX-X, the follicular cells contained granules and vesicles of different sizes and electron densities and a well-developed Golgi apparatus and RER. At developmental stage XI, most follicles were outlined by squamous epithelial cells and presented wide lumens filled with a light colloid. The Golgi complex and RER showed changes in their morphology indicating a decrease in the activity of the thyroid gland. At developmental stage XII, the activity of the embryonic thyroid gradually increased, and at the time of hatching, it exhibited the features of a fully active gland. © 2011 Elsevier GmbH.

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