Electronic and Optical Properties of Cubic SrHfO3

In order to clarify the mechanism of optical transitions for cubic SrHfO₃, we have investigated the electronic structure and optical properties of cubic SrHfO₃ using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties, obtained by minimizing the total energy, are in favorable agreement with the previous work. From the band structure and charge densities as well as the theory of crystal-field and molecular-orbital bonding, we have systematically studied how the optical transitions are affected by the electronic structure and molecular orbitals. Our calculated complex dielectric function is in good agreement with the experimental data and the optical transitions are in accord with the electronic structure.     

Universal critical properties of the Eulerian bond-cubic model

We investigate the Eulerian bond-cubic model on the square lattice by means of Monte Carlo simulations,using an efficient cluster algorithm and a finite-size scaling analysis.The critical points and four critical exponents of the model are determined for several values of n.Two of the exponents are fractal dimensions,which are obtained numerically for the first time.Our results are consistent with the Coulomb gas predictions for the critical O(n) branch for n < 2 and the results obtained by previous transfer matrix calculations.For n=2,we find that the thermal exponent,the magnetic exponent and the fractal dimension of the largest critical Eulerian bond component are different from those of the critical O(2) loop model.These results confirm that the cubic anisotropy is marginal at n=2 but irrelevant for n < 2.     

漫反射立方腔单次反射平均光程的理论和实验研究

根据Beer-Lambert定律可知,增加气体池的有效光程是提高气体监测灵敏度最直接而有效的途径.通过实验研究和分析,漫反射立方腔作为气体池能显著地增加有效光程,因此研究其内部的光线传播规律具有重要意义.基于对漫反射立方腔内光线传播规律的理论分析,得到了单次反射平均光程的理论值,建立了漫反射立方腔内光线传播的理论近似模型,并通过有限元法仿真获得了单次反射平均光程的模拟值.利用可调谐二极管激光吸收光谱技术得到了立方腔的有效光程,间接求得了单次反射平均光程的实验值.对理论值、模拟值和实验值进行比较分析,验证了理论近似模型和有限元法仿真的准确性和稳定性.     

高温高压下cBN单晶转变机理的密度泛函理论研究

为研究Li3N-hBN体系中cBN单晶的转变机理,本文采用基于密度泛函理论的赝势平面波方法和广义梯度近似法(GGA)系统计算了高温高压条件下hBN和cBN的低指数晶面的晶面能,分析了hBN和cBN各晶面之间的能量关系.结果表明:在1800K,5.5 GPa和2000 K,6.0 GPa下,hBN的(1010)晶面与cBN的(100)晶面的相对晶面能差分别为0.7;和1.2;,两组晶面的晶面能连续,即微观上电子密度连续.根据改进后的密度泛函理论(TFDC)可知,hBN能够向cBN直接转变.因此推断:在Li3N-hBN体系中,以Li3N为触媒,cBN单晶是由hBN直接转变而来.     

钫原子磁偶极超精细结构常数及其同位素的磁偶极矩的理论计算

应用基于B样条基组的相对论耦合簇理论方法,计算了~(212)Fr原子的n S (n=7—12), n P (n=7—12)和n D (n=6—11)态的磁偶极超精细结构常数.与精确实验值的比较说明这套理论方法能精确计算出磁偶极超精细结构常数,其中7P态的磁偶极超精细常数的理论值与实验值之间的差异小于1%.在忽略场移效应对Fr原子7P态超精细结构常数的影响下,通过结合实验值进一步定出了~(207-213,220-228)Fr核磁偶极矩μ,这些值与已有的测量值具有非常好的一致性.本文报道了12S, n P (n=9—12)和n D (n=10—11)态的磁偶极超精细结构常数.     

多曲面反射体的计算机辅助设计及优化

研究了自由曲面反射式照明系统的设计理论和方法.根据反射器的尺寸、位置以及配光要求按点光源设计得到曲面型值点初始坐标后,将双三次B样条曲面引入照明系统的设计,反算出控制顶点.给出了空间任意一条入射光线与反射器区块的交点及其曲面法线向量的求法,为了提高光路追迹的效率,针对多曲面反射体给出了一种快速判断相交区块的算法.探讨了用阻尼最小二乘法对B样条曲面反射器进行优化设计的方法,通过优化运算修正控制顶点Z轴坐标,使得曲面在使用扩展光源时光形分布尽可能满足设计要求.     

Luminescence of samarium-activated cubic boron nitride

Under high pressure conditions, we have obtained samples of samarium-activated cubic boron nitride in the form of micropowders, ceramic samples, and polycrystals having high-intensity discrete photoluminescence in the red region of the spectrum that is stable in the temperature range 6 K to 300 K and is assigned to internal f-f electronic transitions in the Sm³⁺ ions. The materials obtained on the basis of cBN are intended for use as phosphors and light emitters (sources of red light) having thermal and chemical stability. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 88–93, January–February, 2008.     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95(过渡金属元素T=Mn，Fe，Co，B，Al，Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现，不同金属T替代Fe，Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95，合金具有相同的MgCu₂型立方Laves相结构；Al，Ga替代使Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴，即自旋重取向，B，Mn，Co替代未使易磁化轴发生明显转动；Al，Ga元素替代使超精细场H_hf略有下降，B，Mn替代对超精细场H_hf的影响不大，而Co元素替代使超精细场H_hf有较大增加；所有元素替代使同质异能移IS有所增加；B，Al，Ga和Mn替代使四极劈裂Q_s增加，而Co替代使四极劈裂Q_s下降. 关键词： 立方Laves相 自旋重取向 穆斯堡尔谱