The cell structures and mechanical properties (i.e., hardness, Young's modulus , shear modulus , and Poisson's ratio) of (Hf 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C (HEC) and (Hf 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )N (HEN) high-entropy ceramics were simulated by special quasi-random structure (SQS) and general random structure (GRS) with atomic occupation preference based on the first-principles density functional theory. The results show that compared to SQS, the cell structure constructed by GRS is more realistic, which is verified via scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive spectroscopy. The mechanical properties simulated by GRS were also determined by microhardness and dynamic elastic modulus testers. The hardness, Young's modulus，shear modulus and Poisson's ratio predicted by GRS are 23.07 GPa, 449.71 GPa, 183.28 and 0.227 for HEC and 22.96 GPa, 413.71 GPa, 162.47 and 0.241 for HEN, which are in a reasonable agreement with the measured results (i.e., 22.05 ± 0.32 GPa, 433 ± 12 GPa, 172 ± 18 GPa, 0.21 for HEC and 22.12 ± 0.13 GPa, 372 ± 23 GPa, 158 ± 11 GPa, 0.23 for HEN). This work can provide a promising reference for preparing high-entropy non-oxide ceramics via the prediction.
Squalene plays a crucial role in plant growth, development, and stress tolerance. To select the best reference genes (RGs) for expression profile analysis of genes involved in squalene biosynthesis in olives under stress tolerance, the expression stability of 22 candidate RGs across four tissues (root, stem, leaf, and fruit) and five representative cultivars under drought stress was assessed using six methods. Our study showed that, ubiquitin-conjugating enzyme1 ( UBC1 ) and 60S ribosomal protein L18-2-like ( 60S ) were the most stable RGs across five different cultivars and various tissues. Additionally, elongation factor 1-alpha-like ( EF1-α2) and UBC1 were the most stable RG in olives under drought stress. UBC1 was the appropriate RG for further study, qPCR analysis showed that five certain genes involved in the squalene biosynthesis exhibited significant differential expression under varying conditions. Specially, the expression level of squalene synthase (SQS) in the leaves was highest, and HPLC analysis showed that squalene content was the highest in leaves. Likewise, the expression levels of SQS and farnesyl diphosphate synthase ( FPPS ) in the leaves of the cultivar Arbosana and Chelmsford Lal were significantly higher than those of the other cultivars, respectively, and HPLC analysis also showed that squalene content was highest in the two cultivars. Interestingly, the amount of squalene increased dramatically in olive under drought stress, as lupeol synthase ( LUPS ) was significantly up-regulated. To date, this study firstly provided the comprehensive analysis of RGs related to squalene biosynthesis in various cultivars and tissues of olives under drought stress.
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