排序方式： 共有5条查询结果，搜索用时 0 毫秒
1
1.
This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO3 by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO3 is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO3 is a promising dielectric material. 相似文献
2.
额济纳盆地地下水盐化特征及机理分析 总被引：7，自引：10，他引：7
运用水文地球化学方法,分析额济纳盆地不同含水层地下水盐化特征及其机理。结果表明:额济纳盆地地下水受水文地质条件的制约,潜水的盐化自沿河主要补给区到蒸发排泄区具有明显的分带性,由河流主要补给区向北和向东西两侧,至居延海,进素土海子和古日乃湖中心洼地地下水,地下水由淡水,逐渐过渡为微咸水、中度咸水及极度咸水、盐水;承压水属于微咸水。依据地下水中各离子含量的比值特征的分析结果,控制本区地下水盐化的主要因素为硅酸盐矿物溶解和蒸发沉积作用,硅酸盐矿物溶解主要发生在沿河的地下水补给区;蒸发沉积作用主要发生在地下水径流-排泄区。深层地下水埋藏较深,蒸发的作用大大减弱,因而含盐量少,水质较好。 相似文献
3.
The TiO2--Mn--TiO2 multilayers are successfully grown on glass and silicon substrates by alternately using radio frequency reactive magnetron sputtering and direct current magnetron sputtering. The structures and the magnetic behaviours of these films are characterised with x-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer, and superconducting quantum interference device (SQUID). It is shown that the multi-film consists of a mixture of anatase and rutile TiO2 with an embedded Mn nano-film. It is found that there are two turning points from ferromagnetic phase to antiferromagnetic phase. One is at 42 K attributed to interface coupling between ferromagnetic Mn3O4 and antiferromagnetic Mn2O3, and the other is at 97 K owing to the interface coupling between ferromagnetic Mn and antiferromagnetic MnO. The samples are shown to have ferromagnetic behaviours at room temperature from hysteresis in the M--H loops, and their ferromagnetism is found to vary with the thickness of Mn nano-film. Moreover, the Mn nano-film has a critical thickness of about 18.5 nm, which makes the coercivity of the multi-film reach a maximum of about 3.965times 10 - 2 T. 相似文献
4.
TiO2 nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol-gel process, and were annealed at 500 ℃ and 800 ℃ in air for 2 hrs. X-ray diffraction (XRD) measurements indicate that the Mn-TiO2 nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 ℃ are of pure anatase and rutile, respectively. The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO2 crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron (BMP) theory, is detected in the Mn-TiO2 samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 ℃ is stronger than that of the sample treated at 800 ℃. The UV-VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO2 powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping. 相似文献
5.
黑河流域水资源的统一管理与承载能力的提高 总被引：16，自引：12，他引：16
黑河流域中、下游水资源利用矛盾十分尖锐，利益调整也极为复杂，1999年成立了黑河流域管理局，为实现以流域为单元，进行统一规划、统一调度、统一管理，建立权威、高效、协调的流域管理体制创造了条件，并在2000年和2001年实施“全线闭口、集中下泄”全流域水资源定量分配。实践证明只要掌握山区水资源动态、实施退耕还林还草与退水、从农业节水开发流域水资源潜力，完全可以取得成功。尽管在实施国务院批准的跨省区的分水方案时，还存在诸多困难，但只要加紧采取“保护上游、整治中游、拯救下游”的综合治理、强化全流域水资源统一管理、加快流域全面节水步伐、加大科技投入等四方面措施，就能突破流域水资源瓶颈障碍，力求不增加流域消耗水量，而达到经济增长，并使流域生态系统逐步走向良性循环。 相似文献
1