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51.
用提拉法生长了Lu2Si2O7:Ce晶体,对该晶体的闪烁性能进行了研究。透射光谱表明,Lu2Si2O7:Ce晶体的吸收边比Lu2SiO5:Ce晶体向短波方向移动了25nm,使透光范围进一步拓宽。X射线发射光谱和UV激发发射光谱均具有典型的双峰特征,主峰在378nm。UV激发发射谱具有温度效应,即375K以上时,发光效率迅速降低;425K以上时,发光主峰位明显红移。衰减曲线符合单指数式衰减规律,常温下经UV激发后的衰减时间约为34ns。从曲线形态看,375K以下的衰减谱与室温下的几乎完全相同,拟合的结果在32.8~34ns之间;衰减时间的温度效应从375K开始显现,即随温度的升高,衰减时间有加速变短的趋势,到500K时缩短为6.72ns。热释光谱在488,553K处有两个热释光峰,但室温附近几乎观察不到热释光峰。 相似文献
52.
53.
Time-domain numerical computation of noise reduction by diffraction and finite impedance of barriers
Chang Woo Lim 《Journal of sound and vibration》2003,268(2):385-401
A new time-domain numerical method is presented for the estimation of noise reduction by the diffraction and finite impedance of barriers. High order finite difference schemes conventionally used for computational aeroacoustics, and time-domain impedance boundary conditions are utilized for the development of the time-domain method. Compared with other methods, this method can be applied more easily to the problems related to nonlinear noise propagation such as impulsive noise and broadband noise. Linearized Euler equations in Cartesian co-ordinates are considered and solved numerically. Straight and T-shaped barriers with and without surface admittance are calculated. In order to assess the accuracy of this time-domain method, comparison with the results of SYSNOISE software (Ver. 5.3) are made. There are very good agreements between the results of the present time-domain numerical method and the boundary element method of the SYSNOISE software. 相似文献
54.
55.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
56.
The mixed complex [Ni(L)(L')](ClO4)2 has been synthesized using 2-aminoethyl- bi(3-bi-aminopropyl)amine with phen (1,10-phenanthroline) in the presence of Ni(II) ion, and its structure was determined by X-ray diffraction. The crystal crystallizes in monoclinic, space group P21/c with a = 13.713(2), b = 13.1466(19), c = 14.780(2) (A), β = 97.620(3)°, V = 2640.9(7)(A)3, F(000) = 1272, Z = 4, Dc = 1.540 g/cm3, R = 0.0536 and wR = 0.1207. The Ni2+ ion is six- coordinated to furnish a distorted octahedral geometry. 相似文献
57.
LIN Chang ZHANG Xiu-Lian 《理论物理通讯》2005,44(2):247-251
The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation. 相似文献
58.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
59.
建立了相变热力学理论和场论的关系. 强调在量子场论中必须引进序参量场, 则相变的讨论就类似于Goldstone bosons 的产生. 如果只讨论一级相变, Goldstone bosons场就足够了; 如果要讨论二级相变, 则必须讨论一系列的场, 这些场构成一个对称群的表示. 另外, 也将这一思想用到色超导中. In this paper we built a relation between the thermodynamical theory of the phase transition and field theory. We emphasized that in the quantum field theory we have to introduce the order parameter fields. Then the discussion of the phase transition is closed to the creation of the Goldstone bosons. If we only discuss the first order transition, the Goldstone bosons fields are sufficient. If we want to discuss the second order transition, we have to discuss a set of fields that constructs a representation of a symmetry group. We also apply this concept to color superconductivity. 相似文献
60.
ZhongJunMA XianLI YangLU ChengWANG QiTaiZHENG 《中国化学快报》2003,14(6):594-596
A novel cycloartane,named sphaerophysone A,9,19-cycloart-7β,24β,25-triol-1-en-3-one,was isolated from the ethanol extract of Sphaerophysa salsula DC.The structure was elucidated on the basis of spectral evidences and confirmed by X-ray analysis,the stereochemistry of the compound was also defined by X-ray analysis. 相似文献