高温高密度氦的压缩特性及其结构的分子动力学模拟

用分子动力学方法和不同参数的指数 6势函数计算了T =30 4K的高密度氦的等温压缩线和能量分布 .给出了能精确描述高密度氦原子间相互作用的指数 6势函数优化参数 .并用优化的势函数计算了高密度氦T =30 0K和T =2 98K的等温压缩线 ,计算结果和实验值非常吻合 .进一步用优化的势函数模拟了高温高密度氦的状态方程及其结构 ,发现当把 ρ限定为 1 .6 0g /cm³ 时 ,其径向分布函数的第 2个峰将在 2 0 0 0～ 30 40K区间消失 ,表明此时发生了固 液相变过程 .     

Oxidation of enones to α′-acetoxyenones using manganese triacetate

The oxidation of α,β-unsaturated ketones with manganese (III) triacetate in benzene furnishes α'-acetoxyenones in good yields.     

A Mössbauer effect study of structural ordering in rapidly quenched Fe–Ga alloys

Samples of Fe_100−xGa_x (x=8.3, 17.9, 20.5 and 23.3) were prepared by rapid solidification from the melt using a single Cu roller. X-ray diffraction studies of all samples showed them to be single phase with the disordered BCC structure. No evidence of superlattice reflections from D0₃ ordering was observed for any of the samples. Room-temperature ⁵⁷Fe Mössbauer effect spectra indicated that all samples were ferromagnetically ordered. Spectra were fit to distributions of hyperfine fields. The x=8.3 sample showed a hyperfine field distribution that was single peaked and indicated a reasonably random distribution of local Fe environments. The x=17.9 and 20.5 samples showed hyperfine field distributions that were bimodal and indicated two distinct local Fe environments. The x=23.3 sample showed three distinct field components. It is suggested that the x=8.3, 17.9 and 20.5 alloys are primarily a disordered BCC phase. The x=8.3 alloy shows a small amount of short-range Ga–Ga pairing, while this short-range pairing is significantly greater in the x=17.9 and 20.5 alloys. The three field components in the x=23.3 alloy correspond well to the two sites associated with the D0₃ phase and a third component corresponding to a remaining L1₂ phase suggesting the presence of at least short-range D0₃ clustering in this alloy.     

Hyperfine magnetic field on Cd-111 in heusler alloys Co2MnZ (Z=Si,Ga, Ge,Sn)

The time differential perturbed angular correlation method has been used to measure, as a function of temperature, the hyperfine magnetic field at Cd sites in the Heusler alloys Co₂MnZ (Z=Si, Ga, Ge, Sn). The hyperfine fields, normalized to the total magnetic moment per formula unit, show an approximately linear trend toward more positive values with increasing lattice parameter.     

多尺度B样条小波边缘检测算子

基于B样条理论提出了一类新的多尺度小波变换,通过其零交叉或模极值能有效地表示和检测信号或图象的边缘,对任意n次B样条,导出了相应的分解和重建的快速算法,对应的用于分解和重建的滤波器的时域和频域响应也被精确地给出.从时频局部化的角度对不同次数的B样条作了分析,认为3次B样条小波在边缘提取等实际应用中是渐近最优的,结果也为B样条小波在立体视觉匹配、滤噪等方面的进一步应用提供了基础.     

An investigation of Fe oxidation states and site distributions in a Tibetan tektite

Room temperature ⁵⁷Fe Mössbauer effect measurements have been used to investigate the local Fe environment and the Fe³⁺/Fe²⁺ ratio in a Tibetan tektite. The spectrum has been analyzed in terms of two quadrupole splitting distributions; one corresponding to Fe²⁺ and one corresponding to Fe³⁺. The Fe²⁺ sites show a mean isomer shift of +1.011 mm/s relative to \alpha-Fe and a mean quadrupole splitting of 1.845 mm/s. The Fe²⁺ quadrupole splitting distribution showed a large peak for positive values, which has been identified with Fe²⁺ with local octahedral coordination, and a smaller peak for negative values, which has been identified with Fe²⁺ with local tetrahedral coordination. The Fe³⁺ sites showed an average isomer shift of +0.20 mm/s and a single peaked quadrupole splitting distribution with a mean near zero. The Fe³⁺/Fe²⁺ ratio, based on the relative areas of the spectra components was found to be 0.015. These results are discussed in terms of those obtained using fitting methods based on discrete sites and other distributions of parameters. Hyperfine parameters for the Tibetan tektite are compared with those obtained for tektites from other regions of the Australasian strewn field. All tektites studied show similar quadrupole distributions and similar mean hyperfine parameters. Fe³⁺/Fe²⁺ ratios ranged from 0.005 to 0.036. The relationship of the microstructure of the Tibetan tektite with that of tektites from various regions of the Australasian strewn field is discussed.