Homogenization of plain weave composites with imperfect microstructure: Part II--Analysis of real-world materials

A two-layer statistically equivalent periodic unit cell is offered to predict a macroscopic response of plain weave multilayer carbon-carbon textile composites. Falling-short in describing the most typical geometrical imperfections of these material systems the original formulation presented in (Zeman and \v{S}ejnoha, International Journal of Solids and Structures, 41 (2004), pp. 6549--6571) is substantially modified, now allowing for nesting and mutual shift of individual layers of textile fabric in all three directions. Yet, the most valuable asset of the present formulation is seen in the possibility of reflecting the influence of negligible meso-scale porosity through a system of oblate spheroidal voids introduced in between the two layers of the unit cell. Numerical predictions of both the effective thermal conductivities and elastic stiffnesses and their comparison with available laboratory data and the results derived using the Mori-Tanaka averaging scheme support credibility of the present approach, about as much as the reliability of local mechanical properties found from nanoindentation tests performed directly on the analyzed composite samples.Comment: 28 pages, 14 figure

Interpretace volebních výzkumů veřejného mínění

The thesis examines election polls media coverage with the goal to understand the structure of the polls media coverage, describe its problems, and contribute to their elimination. Using the framework of news values and commercial news values, the matter is first examined by content analysis on the case of the 2021 elections to the Czech Chamber of Deputies online media coverage. The polls are found to be extensively covered by the Czech online media. The articles are mostly based on the game metaframe with the metaphors of horse race and theater, limiting the voter agency. The greatest emphasis is assigned to calling winners of the polls, changes in the support, and 5% threshold. Unfortunately, most of the poll results are misinterpreted; the common mistake is the illusion of certainty attributed to the poll results. The content analysis findings are adopted by the experimental poll misinformation corrector design. The corrector is a human assisted Twitter robot that finds relevant media tweets about polls and corrects potential misinformation via Twitter replies. The corrector - detecting the illusion of certainty when declaring poll leaders, and results around 5% - aims to educate the actors and contribute to improving the poll media coverage.Práce zkoumá mediální zpravodajství o volebních průzkumech s cílem pochopit strukturu mediálního pokrytí průzkumů, popsat jeho problémy a přispět k jejich odstranění. S využitím rámce zpravodajských hodnot a komerčních zpravodajských hodnot je problematika nejprve zkoumána obsahovou analýzou na případu zpravodajství online médií před volbami do Poslanecké sněmovny PČR v roce 2021. Analýza zjišťuje, že volební průzkumy jsou v českých online médiích hojně pokrývány. Články o nich jsou většinou založeny na herním metarámci s metaforami dostihů a divadla, což omezuje pohled na volby jako výsledek vůle voličů. Největší důraz je přisuzován označování vítězů voleb, změnám podpory a 5% hranici. Většina výsledků průzkumů je bohužel dezinterpretována; častou chybou je iluze jistoty, která je výsledkům průzkumů přisuzována. Závěry obsahové analýzy přejímá experimentální návrh korektoru dezinformací z průzkumů. Korektor je twitterový robot s lidskou asistencí, který vyhledává relevantní mediální tweety o průzkumech veřejného mínění a opravuje případné dezinformace prostřednictvím odpovědí na Twitteru. Korektor - detekující iluzi jistoty při vyhlašování lídrů průzkumů a výsledky kolem 5 % - má za cíl vzdělávat aktéry a přispět ke zlepšení medializace průzkumů.Katedra sociologieDepartment of SociologyFaculty of ArtsFilozofická fakult

Dilema: proizvoditi lijepljene ili piljene drvene grede?

This article gives an overview of the contemporary development of wood production in the Czech Republic with the focus on the production of static structural members. This issue refers to literary sources of several authors dealing with the history and development of sawmills and adaptations of production strategies to the current trends. The study is based on information collected and assessed during the sawmill operations used by wood processing companies to make strategic decisions. Interaction of these input data and information acquired from the available literature indicates the possibility of development and specialization of the existing sawmills in upcoming years. Nearly 20 per cent of round timber is processed into static structural members, wooden beams. Considering the rising prices of input raw material, the question of the extent of cost-effectiveness and economy of sawn structural members arises. This article is aimed to clarify the seissues and compare the production costs of sawn and glued structural members used in common wooden constructions, such as roof frames, prefabricated houses, etc. This may have an impact not only on sawmills but also on the extent of use of this type of wooden construction products. The question is whether the new restructuring of sawmills is coming or not?U radu se daje pregled suvremenog razvoja drvne proizvodnje na području Republike Češke, s naglaskom na proizvodnju statičkih strukturnih elemenata. U pregledu se navode radovi nekoliko autora koji obrađuju povijest i razvoj pilana te strateške prilagodbe proizvodnje trendovima. Studija se koristi informacijama prikupljenima tijekom proizvodnje u pilani, na temelju kojih tvrtke za preradu drva donose strateške odluke. Povezivanjem tih ulaznih podataka i informacija iz dostupne literature dobiva se perspektiva razvoja i specijalizacije suvremenih pilana u idućim godinama. Gotovo 20 % volumena oblog drva prerađuje se u statičke strukturne elemente – drvene grede. S obzirom na rast cijena ulazne sirovine, postavlja se pitanje isplativosti i ekonomičnosti proizvodnje piljenih strukturnih elemenata.Cilj je ovog članka objasniti tu problematiku i usporediti troškove proizvodnje piljenih i lijepljenih strukturnih elemenata koji se obično upotrebljavaju u drvenim konstrukcijama kao što su krovne konstrukcije, montažne kuće i sl. To može utjecati ne samo na proizvodnju u pilanama, već i na masovnost uporabe takvih vrsta drvenih građevnih proizvoda. Pritom se nameće pitanje hoće li doći do novog preustroja pilana ili ne

Podstata nového chápania výchovy a vzdelávania v prírodovednom úseku

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Selected topics in homogenization of transport processes in historical masonry structures

The paper reviews several topics associated with the homogenization of transport processed in historical masonry structures. Since these often experience an irregular or random pattern, we open the subject by summarizing essential steps in the formulation of a suitable computational model in the form of Statistically Equivalent Periodic Unit Cell (SEPUC). Accepting SEPUC as a reliable representative volume element is supported by application of the Fast Fourier Transform to both the SEPUC and large binary sample of real masonry in search for effective thermal conductivities limited here to a steady state heat conduction problem. Fully coupled non-stationary heat and moisture transport is addressed next in the framework of two-scale first-order homogenization approach with emphases on the application of boundary and initial conditions on the meso-scale.Comment: 19 pages, 13 figures, 2 table

Preliminary results on intersexual differences in gene expression of chemokine K203 in mononuclear cells of chicken

Sex steroid levels increase during sexual maturation and cause alterations in many physiological and morphological traits. Some of these changes may be connected with age-dependent and intersexual differences in the immune system. This topic is still insufficiently understood, especially in avian species, partially due to methodological limitations. In this study we measured the gene expression of proinflammatory cytokines (IL-1β, IL-6, IL-18) and chemokines [K60 (IL-8-like chicken chemokine — CXCLi1), CAF (IL-8-like chicken chemokine — CXCLi2), and K203] in mononuclear cells isolated from blood and spleen after in vitro stimulation with lipopolysaccharide (LPS). Samples were collected from chickens at two ages (from pullets before sexual maturity and from sexually mature egglaying hens). After LPS stimulation, a substantial increase was recorded in the gene expression of IL-6 and K203. All other measured genes were expressed at low levels in mononuclear cells irrespective of cell sources. We found a trend toward intersexual differences in K203 expression, but the expression of other cytokines and chemokines did not differ between the two sexes. The effect of stimulation was more pronounced in monocytes than in spleen macrophages, mainly in IL-6, IL-1β and K203 gene expression. Our findings represent a basis for further studies on the effects exerted by sexual hormones on the immune phenotype of birds

Phase-field Fracture Modelling of Thin Monolithic and Laminated Glass Plates under Quasi-static Bending

A phase-field description of brittle fracture is employed in the reported four-point bending analyses of monolithic and laminated glass plates. Our aims are: (i) to compare different phase-field fracture formulations applied to thin glass plates, (ii) to assess the consequences of the dimensional reduction of the problem and mesh density and refinement, and (iii) to validate for quasi-static loading the time/temperature-dependent material properties we derived recently for two commonly used polymer foils made of Polyvinyl Butyral or Ethylene-Vinyl Acetate. As the nonlinear response prior to fracture, typical of the widely used Bourdin-Francfort-Marigo model, can lead to a significant overestimation of the response of thin plates under bending, the numerical study investigates two additional phase-field fracture models providing the linear elastic phase of the stress-strain diagram. The typical values of the critical fracture energy and tensile strength of glass lead to a phase-field length-scale parameter that is challenging to resolve in the numerical simulations. So, we show how to determine the fracture energy concerning the applied dimensional reduction and the value of the length-scale parameter relative to the thickness of the plate. The comparison shows that the phase-field models provide very good agreement with the measured stresses and resistance of laminated glass, despite the fact that only one/two cracks localised using the quasi-static analysis, whereas multiple cracks evolved during the experiment. It has also been observed that the stiffness and resistance of the partially fractured laminated glass can be well approximated using a 2D plane-stress model with initially predefined cracks, which provides a better estimation than the one-glass-layer limit.}Comment: 29 pages, 20 figures, and 6 table