The aim of my article will be the analysis of the results of the empirical research concerning the process of acquisition of English article system by Polish learners, carried out at three different levels of L2 acquisition.

English articles, as a semantic category non-existent in Polish, constitute a notorious source of difficulties in their acquisition by Poles. Polish learners of English at the beginning of their education, being at the elementary level, do not actually acquire articles because of the lack of associations with Polish counterparts. The semantics of English articles differs while compared to Polish, where instead of the articles: a/an, the demonstrative pronouns occur, e.g. ten (this), tamten (that) or there exists a different word order, different intonation, verbal aspects and many other syntactic-semantic processes.

While teaching English, we may easily observe that the process of acquisition of English article system by Polish learners differs depending on the level of advancement in learning English. In my article I would like to familiarize the addressees with the question of acquisition of articles by young teenagers, late teenagers and young adults. I hope the results of my research will evoke an interesting source for scientific discourse.

Emerging researches in humans, pigs and mice, highlighted that estrogen plays a pivotal role in self-renewal and differentiation of bone marrow mesenchymal stem cells (BMSCs). The present study aimed at evaluating effects of 17 beta-estradiol (E2) on proliferation and apoptosis of canine-derived bone marrow mesenchymal stem cells (cBMSCs) in vitro. The results showed that E2 supplementation at the concentration of 10-11 M promoted the proliferation of cBMSCs by CCK-8 assay and RT-qPCR analysis for the proliferation-related genes, with proliferating cell nuclear antigen (PCNA), cyclin-D1 (CCND1) being up-regulated and cyclin-dependent kinase inhibitor 1B (CDKN1B) being down-regulated. Contrarily, analysis of fluorescence-activated cell sorting (FACS) and RT-qPCR demonstrated that E2 supplementation above 10-11 M had inhibitory effects on the proliferation of cBMSCs and induced apoptosis. Intriguingly, cBMSCs still possessed the capability to differentiate into osteoblasts and adipocytes with 10-11 M E2 addition. Taken together, this study determined the optimal culture condition of cBMSCs in vitro, and has important implications for further understanding the regulatory effect of E2 on the self-renewal of cBMSCs, which are helpful for the clinical application of BMSCs.

Compositional and textural data are presented for zircon, secondary Zr-silicates, catapleiite and elpidite in a peralkaline granite from the Ilímaussaq complex, south Greenland. The zircon is essentially stoichiometric, with (Zr + Hf + Si) = 1.96–1.98 a.p.f.u. The secondary Zr-silicates show a wide range of Zr/Si atomic ratios (0.13–0.79). The catapleiite varies from close to stoichiometric to a Na-depleted type showing cation deficiency (5.2–5.8 a.p.f.u.). Elpidite shows similar variations (7.2–9.0 a.p.f.u.). Textural relationships between the Zr phases are interpreted to show that magmatic zircon interacted with hydrous fluids exsolved from the magma to form the secondary Zr-silicates. Formation of catapleiite was late‑magmatic, in equilibrium with a Na-Sibearing fluid. This was followed by the crystallization of elpidite, the fluid having a different Na/Si ratio. Both catapleiite and elpidite experienced Na-loss during late-stage hydrothermal alteration.

In generalized method of data reconciliation as equations of conditions beside substance and energy balances can be used equations which don’t have precisely the status of conservation lows. Empirical coefficients in these equations are traded as unknowns’ values. To this kind of equations, in application of the generalized method of data reconciliation in supercritical power unit, can be classified: steam flow capacity of a turbine for a group of stages, adiabatic internal efficiency of group of stages, equations for pressure drop in pipelines and equations for heat transfer in regeneration heat exchangers. Mathematical model of a power unit was developed in the code Thermoflex. Using this model the off-design calculation has been made in several points of loads for the power unit. Using these calculations identification of unknown values and empirical coefficients for generalized method of data reconciliation used in power unit has been made. Additional equations of conditions will be used in the generalized method of data reconciliation which will be used in optimization of measurement placement in redundant measurement system in power unit for new control systems

Presented in this paper are results of an experimental investigation on the rivet flexibility and load transmission in a riveted lap joint representative for the aircraft fuselage. The test specimens consisted of two aluminium alloy Alclad sheets joined with 3 rows of rivets. Two different squeeze forces were applied to install the rivets. Rivet flexibility measurements have been performed under constant amplitude fatigue loading using several methods including two original optical techniques developed by the present authors. The axial tractions in the sheets required to determine the rivet flexibility have been derived from strain gauge measurements. In order to eliminate the effect of secondary bending the strain gauges have been bonded at the same locations on the outside and faying surface of the sheet. The experiments enabled an evaluation of the usefulness of various techniques to determine the rivet flexibility. It was observed that, although the measured flexibility was identical for both end rivet rows, the load transfer through either of these rows was different. Previous experimental results by the present authors suggest that behind the non-symmetrical load transfer distribution through the joint are large differences between the rivet hole expansion in the sheet adjacent to the driven rivet head and the sheet under the manufactured head [1]. It has been concluded that commonly used computation procedures according to which the load transfer is only related to the rivet flexibility may lead to erroneous results.