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Spool valve leakage behaviour

100%

Gordic D. , Babic M. , Milovanovic D. , Savic S.

tom Vol. 11, no 4

859-866

A four-way axial spool servovalve has such a design that flows through its restrictions can be presented by means of a hydraulic bridge. The characteristics analytically describe the fluid flow through spool orifices in the most of working regimes. The exceptions are regimes around the null characterized by an overlap existence when internal leakages dominate. Several mathematical models for the calculation of the internal leakage flows are presented in this paper including theoretical model worked out by authors. Modelling results are compared with appropriate experimental.

Czterodrogowy rozdzielacz hydrauliczny ma budowę, w której przepływ przez jego kanały może być przedstawiony (opisany) za pomocą tzw. mostku hydraulicznego. Z reguły charakterystyki zaworu opisują przepływ cieczy przez szczeliny dla większości stanów jego pracy. Wyjątkiem są stany pracy, w których dominują wewnętrzne przecieki. W pracy przedstawiono modele matematyczne do obliczeń wewnętrznych przecieków. Przedstawiono propozycję modelu teoretycznego opracowanego przez autorów. W pracy przedstawiono również porównanie wyników badań symulacyjnych z odpowiednimi badaniami eksperymentalnymi.

Age-related changes in the myenteric plexus of the human jejunum

75%

Mandic P. , Lestarevic S. , Filipovic T. , Savic S. , Stevic S. , Kostic M.

nr 2

The structural characteristics of photoageing in mice caused by the effects of ultraviolet A radiation

75%

Savic S. , Smiljic S. , Lestarevic S. , Ilic A. , Mijovic M. , Mandic P. , Djerkovic B.

nr 3

Background: Due to its deep penetration into the dermis, ultraviolet A (UVA) radiation is considered a primary factor in skin photoageing. The aim of this study is to use a qualitative and quantitative analysis to determine the structural parameters of skin photoageing in mice exposed to UVA radiation, with or without the application of a photoprotective cream. Materials and methods: The experiment consisted of the radiation of female BALBc mice in a solarium by UVA rays, up to total dosages of 7800 J/cm² and 12500 J/cm². A total of 78 animals were divided into four experimental and two control groups. All animals were shaved and the animals in two experimental groups were treated with a photoprotective cream half an hour before exposure. The samples of the treated skin were stained with haematoxylin-eosin and Van-Gieson staining methods. All measurements, except for the presence of dyskeratosis, were taken using ImageJ 150i software. Results: In the study, the signs of skin photoageing were more evident in untreated groups of animals. Dyskeratosis was more frequent in both of the untreated groups of animals (p = 0.004 and p = 0.003). The lowest values of epidermal thickness (13.8 ± 2.6 μm and 12.7 ± 2.3 μm) were present in both of the untreated groups of animals (p < 0.001 and p < 0.001). The highest values of stratum corneum thickness (34.3 ± 8.5 μm) were observed in the untreated, shorter radiated group of animals (p < 0.001) which was irradiated for the shortest period of time. Beside the control groups, the highest length of dermo-epidermal junction was recorded in the group of treated, longer radiated animals (1467.6 ± 94.6 μm; p = 0.373). The lowest values of dermal thickness (115.9 ± 10.5 μm and 134.8 ± 21.8 μm) and volumetric density of the collagen fibres (31.92 ± 3.19% and 29.40 ± 4.54%) were present in both untreated groups of animals (p < 0.001, p < 0.001, p = 0.035). Conclusions: Skin photoageing was most pronounced in the groups of animals irradiated without the application of photoprotective cream. (Folia Morphol 2020; 79, 3: 548–556)