RESUMO
Crystallographic characterization, energy band structure, densities of states and charge density, elastic properties, ideal tensile and shear strengths, lattice dynamics and thermophysical characteristics of UGe3 of AuCu3-type have been studied by employing the first principles method based on Density Functional Theory (DFT). The optimized lattice parameters, such as lattice constant a, equilibrium cell volume V0, U-Ge distance and U-U distance of UGe3, are in favorable agreement with the available experimental results. Three single-crystalline elastic constants of C11, C12, and C44 have been obtained using the "energy-strain" technique by increasingly varying small strains. The polycrystalline elastic moduli including volume modulus B, Young's modulus E, and shear modulus G, Poisson's ratio v, brittle/ductile nature, Debye temperature θD, and the integration of elastic wave velocities over different crystallographic directions have also been successfully calculated. The anisotropy of the three-directional bulk modulus and Young's modulus is systematically explored and analyzed. The calculations indicate that UGe3 of AuCu3-type should be stabilized mechanically, and the system possesses insignificant elastic anisotropy. In particular, the vibrational spectrum, phonon densities of states and the infrared-active and inactive vibration modes at the center of the Brillouin zone are determined using Density Functional Perturbation Theory (DFPT) and group theory for the first time. This study reveals that UGe3 of AuCu3-type is also stable dynamically. Finally, within the calculated phonon densities of states and the quasi-harmonic Debye model, the constant volume heat capacity Cv and the vibration entropy S in the temperature range of 0-1000 K are predicted and analyzed comprehensively. The present investigations are expected to provide some valuable references for further exploring the properties of uranium compounds.
RESUMO
We perform detailed first principles calculations of the structural parameters at zero pressure and high pressure, the elastic properties, phonon dispersion relation, and ideal strengths of U2Mo with the C11b structure. In contrast to previous theoretical studies, we show that the I4/mmm structure is indeed a mechanically and dynamically unstable phase, which is confirmed by the negative elastic constant C66 as well as the imaginary phonon modes observed along the Σ1-N-P line. The calculations of ideal strengths for U2Mo are performed along the [100], [001], and [110] directions for tension and on (001)[010] and (010)[100] slip systems for shear load. The ideal shear strength is about 8.1 GPa, much smaller than a tension of 18-28 GPa, which indicates that the ductile U2Mo alloy will fail by shear rather than by tension.
RESUMO
In this study, a pot experiment was carried out to examine the effects of high CO2 concentration, drought and interaction on seedling growth traits, biomass accumulation and physiological characteristics of different stay-green wheat seedlings, with a stay-green wheat variety Yannong 19 and a non stay-green wheat variety Hanxuan 3 as test materials. There were four treatments in the Open Top Chamber with factorial of CO2 concentration (370 µmol·mol-1 vs 550 µmol·mol-1) and drought (45%-55% vs. 75%-85% of field water-holding capacity). Drought significantly inhibited the growth and development of wheat seedlings, while CO2 concentration significantly increased the number of tillers and promoted the growth and development of wheat seedlings. Under drought condition, high CO2 concentration increased the number of tillers of Hanxuan 3 and Yannong 19 by 61.0% and 42.3%, respectively. Under both water conditions, high CO2 concentration significantly increased the biomass of wheat seedlings, and decreased the content of peroxidase and proline in leaves. Under drought condition, high CO2 concentration showed stronger "fertilizer effect". Furthermore, different varieties had different responses to high CO2 concentration, with higher sensitivity of Hanxuan 3 to enhancement of CO2 concentration. Under the scenario of increasing CO2 concentration, the amount of irrigation water applied to a field can be appropriately reduced for efficient use of water resources. Meanwhile, it is necessary to pay attention to the selection of suitable wheat varieties.
Assuntos
Secas , Plântula , Atenção , Dióxido de Carbono , Triticum , ÁguaRESUMO
Taking 7 local wheat varieties in Shanxi Province of China and two other control varieties as test materials, this paper studied their morphological and physiological traits under normal and water stress field conditions. The drought-resistance coefficient of each index of the traits was calculated. On the basis of principal component analysis, the correlations between the drought-resistance indices and their relationships with the drought-resistance of different varieties were analyzed by GGE biplot, and the drought resistance of the wheat varieties was comprehensively evaluated with the combination of subordinate function and drought resistance index analysis. The main morphological and physiological factors affecting the drought-resistance of the wheat varieties were uppermost internode length, plant height, internode length, leaf area, leaf POD and SOD activities, and leaf relative water content and relative electric conductivity. There existed different degrees of correlation between these indices, and each index had different effects on the drought resistance of the varieties, being the main cause for the different drought resistance of the wheat varieties. Based on the drought-resistance, the test varieties could be classified into three groups, i. e. , drought-resistance group, intermediate group, and sensitive group. Two highly drought-resistance cultivars, Baiheshangtou and Zhuganqing, whose drought-resistance was similar to that of drought-resistant Jinmai 47, could be used as the parent materials for breeding drought-resistance wheat.