巨磁阻材料Sr1.9 Gd0.1FeMoO6光掺杂的正电子湮没研究

采用固相反应法制备Sr1.9Gd0.1FeMoO6样品,通过X射线衍射检验其为单相.在光照10、20、30、40min后分别做了正电子湮没实验.研究了正电子寿命与先掺杂量之间的变化关系,分析了光掺杂对样品电子结构的影响.结果表明:正电子寿命参数对光掺杂量十分敏感,τ1、τ2随光照时间具有相同的变化趋势;在光照时间t>20 min时,平均电子浓度随光照时间有明显的变化;持续的光掺杂使样品缺陷的平均尺寸相对减小,可能由微空洞、多空穴向双空穴或单空穴转变,使电子结构趋于有序化.     

沃尔什函数排列问题的研究

本文着重分析了沃尔什函数W、P、H排列之外的第四种排列方式,并给出了四种排列沃尔什函数明确的统一定义式及它们之间的序数转换表。     

Configurations, Electronic Structure and Magnetic Ordering of Small Manganese Clusters

We investigate the configurations, electronic structures, and magnetic ordering of MnN （N = 2-13） clusters based on all-electron density functional theory. The Jahn-Teller effect plays an important role in determining the ground state of certain geometries. The magnetic ordering of the MnN dusters transits from ferromagnetic ordering for the smallest （ N = 2, 3） dusters to a near degeneracy state including ferromagnetic and ferrimagnetic ordering in the vicinity of N = 4-6 and to a clear ferrimagnetic ordering at N = 7 or beyond. N = 6 and 10 are the magic numbers for neutrai MnN （N = 2-13） dusters.     

Structural and magnetic properties of BiFe_(1-x)Cr_xO_3 synthesized samples

Chromium doping effects on the structure and the magnetic properties of bismuth ferrite BiFe1-xCrxO3 （x = 0-0.3） （BFCxO） polycrystalline samples are examined. The Perovskite-type oxide samples are synthesized by the conventional solid state reaction at a high pressure of 7 GPa and a temperature of 1273 K. The X-ray powder diffraction patterns at room temperature show that all the samples with x = 0.0-0.3 are described by the rhombohedral structure. In the meantime, it is revealed that the doping of Cr can induce noticeable lattice distortions in the doping samples, and the largest distortion is observed in the case x = 0.1. The magnetic hysteresis loops measured at room temperature exhibit week ferromagnetic behaviors of the samples and the magnetization is found to increase with the increase in Cr concentration. The temperature- dependent magnetization curves indicate antiferromagnetic features in samples. Moreover, Cr-doping tends to reduce the ordering temperature.     

知觉组合规律的概率分布及信息熵

知觉组织过程中有数条知觉组合规律,这些定性规律决定了场景中的元素如何组合在一起,形成形状、运动和空间分布等整体上的知觉.研究了知觉组合规律定量描述的理论问题,给出了与之相对应的概率分布及信息熵,定量验证了知觉组合规律的正确性,并且给出了知觉组合的自上而下信息加工的概率分布方法.