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Experimental Analysis of the Tensile Properties of Painting Canvas

100%

Penava Ž. , Šimić-Penava D. , Tkalec M.

tom Vol. 16, no. 4

182--195

In this paper, the practical application of uniaxial testing of painting canvas for determining its mechanical properties is presented. Painting canvases have a complex composite structure whose mechanical properties are considerably improved in relation with the initial basic material. Painting canvas or coated fabrics are obtained by applying a certain number of coatings to raw fabrics. Experimental testing and determining mechanical properties of painting canvas under tensile force at different angles in relation to the weft direction are discussed in the paper. The fabrics were tested before coating, as well as after one, two and three coatings. The values of tensile force in relation to relative extension of coated textiles were measured, as well as breaking force values, elongation at break, contraction at break, work to rupture. Based on the experimentally obtained values, modulus of elasticity, Poisson’s ratio and the level of anisotropy of the coated textile materials were calculated. The experimental results demonstrate the applicability of theoretical formulae. The number of coated layers on the raw fabric exerts a significant impact on the Poisson’s ratio. The values of breaking force, elongation at break, work to rupture and modulus of elasticity increase with an increase in the number of coated layers, and at the same time coefficient of anisotropy decrease. It has been shown that by increasing the number of coated layers in a coated material, its anisotropic properties decrease, while isotropic properties increase. With an increase in the number of coatings, the differences between experimental and theoretical values of modulus of elasticity decrease.

The acclimation of carnivorous round-leaved sundew (Drosera rotundifolia L.) to solar radiation

100%

Tkalec M. , Dobos M. , Babic M. , Jurak E.

tom 37

nr 04

Round-leaved sundew (Drosera rotundifolia L.) is a carnivorous plant which inhabits nutrient-poor, moist, and sun-exposed areas such as peat bogs and sandpits. These habitats are threatened by succession which could lead to substantial shading of sundews. Nevertheless, D. rotundifolia can also grow in shaded environment within a layer of dwarf shrubs, indicating great photosynthetic plasticity whose mechanism still remains largely unknown. Therefore, the aim of this experiment was toinvestigate physiological responses involved in D. rotundifolia acclimation to different light levels. Photosynthetic pigment content, photochemical efficiency, and content of phenolic compounds were studied in plants acclimated to sunlight conditions (outdoor-growing plants) as well as in those acclimated to low-light conditions (indoor-growing plants) before and after sudden exposure to high-intensity solar radiation for 5 h per day during 7-day period. Outdoor-growing plants were larger in size, had higher Fv/F0 ratio, reddish leaves, and they flowered. Also, they had higher content of phenolic compounds including flavonoids and anthocyanins, as well as higher Car/Chl ratio, while indoor-growing plants showed higher chlorophyll a and b content. There was no significant difference in the photochemical efficiency of PSII between indoor- and outdoor-growing plants. The indoor-growing plants that were exposed to solar radiation showed initial photoinhibition of photosynthesis. However, after 7-day exposure, the chlorophyll content significantly decreased while contents of carotenoids, flavonoids, and anthocyanins, as well as Car/Chl ratio increased, leading to the restoration of PSII activity. In conclusion, our results revealed that sundews can successfully acclimate to both low- and highlight intensities by changing content and composition of the photosynthetic pigments and phenolic compounds.

Expression of HSP70 isoforms in Lemna minor exposed to cadmum and salinity

88%

Tkalec M. , Balen B. , Fulgosi H. , Vidakovic-Cifrek Z. , Regula I.

tom 26

nr 3 suppl.