Islamic Azad University

About: Islamic Azad University is a education organization based out in Tehran, Iran. It is known for research contribution in the topics: Population & Adsorption. The organization has 83635 authors who have published 113437 publications receiving 1275049 citations. The organization is also known as: Azad University.

Eshelby–Mori–Tanaka approach for vibrational behavior of continuously graded carbon nanotube-reinforced cylindrical panels

Abstract: In this paper, natural frequencies characteristics of a continuously graded carbon nanotube-reinforced (CGCNTR) cylindrical panels based on the Eshelby–Mori–Tanaka approach is considered. The volume fractions of oriented, straight single-walled carbon nanotubes (SWCNTs) are assumed to be graded in the thickness direction. In this research work, an equivalent continuum model based on the Eshelby–Mori–Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented, straight carbon nanotubes (CNTs). The CGCNTR shell is assumed to be simply supported at one pair of opposite edges and arbitrary boundary conditions at the other edges such that trigonometric functions expansion can be used to satisfy the boundary conditions precisely at simply supported edges. The 2-D generalized differential quadrature method (GDQM) as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The novelty of the present work is to exploit Eshelby–Mori–Tanaka approach in order to reveal the impacts of the volume fractions of oriented CNTs, different CNTs distributions, various mid radius-to-thickness ratio, shell angle, length-to-mean radius ratio and different combinations of free, simply supported and clamped boundary conditions on the vibrational characteristics of CGCNTR cylindrical panels. The interesting and new results show that continuously graded oriented CNTs volume fractions can be utilized for the management of vibrational behavior of structures so that the frequency parameters of structures made of such material can be considerably improved than that of the nanocomposites reinforced with uniformly distributed CNTs.

Interactive effects of drought stress and chitosan application on physiological characteristics and essential oil yield of Thymus daenensis Celak

Abstract: Thymus daenensis , a perennial herb, is often grown in areas that experience drought conditions during its growing period. Application of chitosan may compensate for the negative impact of drought stress on the yield of oil and secondary metabolites in Thymus . The interactive effects of foliar application of chitosan and drought stress on dry matter, essential oil yield, and selected physiological characteristics including photosynthetic pigments, osmotic adjustment, and lipid peroxidation of Thymus were investigated in a two-year study from 2014 to 2015. Treatments consisted of 0, 200, and 400 μL L − 1 chitosan applied to plants grown under field capacity, mild drought stress (50% field capacity), and severe drought stress (25% field capacity). Dry matter yield decreased substantially as drought stress intensified. However, essential oil content increased under stress conditions, with the highest essential oil yield obtained from plants under mild drought stress. Foliar application of chitosan compensated to some extent for dry matter and oil yield reduction of plants grown under drought stress. The highest essential oil yield (1.52 g plant − 1 ) was obtained by application of 400 μL L − 1 chitosan under the mild stress condition in 2015 when plants were mature. The compensatory effect of chitosan in reducing the negative impact of stress conditions on dry matter and oil yield was due mainly to stimulation of osmotic adjustment through proline accumulation and reduction of lipid peroxidase level, which increased the integrity of cell membranes of thyme leaves.