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排序方式: 共有438条查询结果,搜索用时 15 毫秒
291.
M. Hichour D. Rached M. Rabah S. Benalia R. Khenata F. Semari 《Physica B: Condensed Matter》2009,404(21):4034-4038
First-principle calculations of structural, elastic and high pressure properties of antiperovskites XNBa3 (X=As, Sb) are performed, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivatives. We have determined the elastic constants C11, C12 and C44 and their pressure dependence. We derived shear moduli, Young's modulus, Poisson's ratio and Lamé's constants for ideal polycrystalline XNBa3 aggregates. By analyzing the ratio of the bulk to shear moduli, we conclude that XNBa3 compounds are brittle in nature. We estimated the Debye temperature of XNBa3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNBa3 and SbNBa3 compounds, and it still awaits experimental confirmation. 相似文献
292.
G.N. Prata 《Physica B: Condensed Matter》2009,404(19):3151-3154
Ground-state energies for antiferromagnetic Heisenberg models with exchange anisotropy are estimated by means of a local-spin approximation made in the context of the density functional theory. Correlation energy is obtained using the non-linear spin-wave theory for homogeneous systems from which the spin functional is built. Although applicable to chains of any size, the results are shown for small number of sites, to exhibit finite-size effects and allow comparison with exact-numerical data from direct diagonalization of small chains. 相似文献
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This paper deals with the standing wave for a Hamiltonian nonlinear wave equation which can be viewed as a representative of the class of equations of interest. On the one hand, by proving a compactness lemma and solving a variational problem, the existence of the standing wave with ground state for the aforementioned equation is proved. On the other hand, the authors derive the instability of the standing wave by applying the potential well argument, the concavity method and an invariant region under the solution flow of the Cauchy problem for the equation under study, and the invariance of the region aforementioned can be shown by introducing an auxiliary functional and a supplementary constrained variational problem. 相似文献
296.
Sofia KantorovichRudolf Weeber Joan J. CerdàChristian Holm 《Journal of magnetism and magnetic materials》2011,323(10):1269-1272
We present simulations and analytical calculations for a system of magnetic nano-particles that possess a dipole moment that is shifted out of the center of mass, towards the surface, leading to a further asymmetry of the dipolar interaction. In our contribution, we discuss the peculiarities of ground state small clusters, both, with and without an external magnetic field. Small clusters help us to get an insight into the inter-particle interactions and form a building block for studies of larger systems. Without external magnetic field, the ground state structure changes from chains and rings with parallel alignment of moments, usually observed in dipolar particles (Prokopieva et al., 2009 [1]), to pairs and triangles with close to anti-parallel orientation of moments, when the shift of the dipole is increased. We also present magnetization properties of larger systems at finite temperature and observe the influence of the shift in particular on the initial slope of the magnetization curve, namely, the initial susceptibility. 相似文献
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Electric cable (or rope) shovels are critical equipment in the surface mining industry. An improved understanding of the factors which affect the flow of broken material into the dipper during loading can help to evaluate the performance of the excavator, define the criteria for equipment selection and develop ways to mitigate equipment damage caused by broken particles. In this paper, the mechanism of granular material flow was investigated through a series of laboratory tests by moving 1:32 and 1:20 (cube root scale) models of a 44 m3 dipper through a test bin filled with angular crushed limestone. It was found that neither dipper angle nor hoist speed has significant influence on the general flow pattern. It was also found that the general flow mechanism is independent on the size of the dipper. Quantitatively, it was determined that hoist speed and pitch angle affect the productivity of the machine with lower pitch angle resulting in higher payload, and faster hoist speed results in shorter dig time. While both lower pitch angle and faster hoist speeds also produce a higher rate of energy consumption, overall both contribute to improved machine productivity. 相似文献
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