Dynamical properties of two-band superlattices with strong interband coupling in real space under the action of ac and dc－ac fields

Within a two-band tight-binding model driven by ac and dc－ac electric fields, using numerical methods, we investigate the dynamics of electrons and the quasi-energy spectrum of the system with strong interband coupling in real space. We find that when the bandwidth is suppressed to a value much smaller than the field frequency, the dynamical localization can exist in the system. The corresponding regions are found for the occurrence of dynamical localization in the parameter space.     

高维非线性演化方程孤立波的同伦分析法求解

利用同伦分析法求解了修正的Kadomtsev-Petviashvili方程, 得到了它的近似孤立波解, 该解与精确解符合得非常好.结果表明，同伦分析法在求解高维非线性演化方程的孤立波解时, 仍然是一种行之有效的方法. 关键词： 同伦分析法 修正的Kadomtsev-Petviashvili方程 孤立波解     

Structural and upconversion fluorescence properties of Er/Yb-codoped oxychloride lead-germanium-bismuth glass

Structural and infrared-to-visible upconversion fluorescence properties of Er³⁺/Yb³⁺-codoped oxychloride lead-germanium-bismuth glass have been studied. The Raman spectrum investigation indicates that PbCl₂ plays an important role in the formation of glass network, and has an important influence on the upconversion luminescence owing to lower phonon energy. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation.     

Giant Magneto-Impedance of Co50Ni22Ga28 Alloy with High Chemical Ordering

The microstructure of CosoNi22Ga28 ribbon with the L10 structure is examined. The band-like morphology is observed. These bands with the width in a range of 40-200 nm appear along the transverse direction of the ribbon. The giant magnetoimpedance （GMI） effect in this alloy is measured. The results show that Co5oNi22Ga28 exhibits a sharp peak of the GAI effect. The maximum GAH ratio up to 360% is detected. The GMI effect measured versus temperature shows large jumps of the magnetoimpedance amplitude at the reversal martensitic transformation temperature 240℃ and Curie temperature 375℃C respectively. The jump ratios of the magnetoimpedance amplitude examined at these temperatures are about 5 and 10, respectively.     

水热法合成FeS2粉晶及其生长热动力学的研究

采用溶胶_凝胶水热法合成了单相黄铁矿结构的FeS2₂粉晶. 用x射线衍射、傅 氏变换红外光谱等分析手段对FeS2₂粉晶进行了表征，以简化的数学模型及相 变理论讨论了晶体 生长过程. 结果表明：FeS2₂晶粒的生长过程属于相变与扩散的混合机制，符 合经时间 指数修正的二次方动力学方程，是一个生长速率随时间变化的过程；水热晶化温度高于453 K、反应时间超过18 h且有适量的硫参与反应时，可得到单相的黄铁矿型的FeS2₂关键词： 溶胶_凝胶水热法 2粉晶')" href="#">FeS2₂粉晶 晶粒生长 热动力学     

La1-xPrxMnO3(x=0.1,0.2)薄膜庞磁电阻性质的研究

一种新的庞磁电阻氧化物薄膜La1-xPrxMnO3(x=0.1,0.2)薄膜用脉冲激光沉积(PLD)方法生长在(100)SrTiO3单晶基底上.XRD结果显示薄膜具有很好的外延单晶取向.电输运和磁性质的研究表明薄膜具有显著的庞磁电阻效应(CMR)效应,其中磁电阻比率达95%(在5T的磁场下).X射线光电子能谱(XPS)的结果表明薄膜体系中Pr离子的价态为+4价,因此该薄膜很可能是电子掺杂的庞磁电阻体系.     

高压下制备的累托石/酚醛树脂复合材料微结构和热性能研究

 采用物理方法在高压下制备了酚醛树脂（PF）/累托石（REC）纳米复合材料,用X射线衍射（XRD）、透射电子显微镜（TEM）及热分析（DSC/TGA）等方法,研究了复合材料的物相、显微结构以及热学性能。结果表明,不通过层间高分子聚合反应,不预先对累托石进行有机化处理,在高压下,由聚合物分子插入粘土层间,可以形成剥离型树脂/粘土纳米复合材料,并且其热学性能发生了较大的改变。     

Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the Tm^3＋：Lu2SiO5 （Tm：LSO） crystal is grown by Czochralski technique. The roomtemperature absorption spectra of Tm：LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Ω2=9.3155×10^-20 cm^2, Ω4=8.4103×10^-20 cm^2, Ω6=1.5908×10^-20 cm^2, the fluorescence lifetime is calculated to be 2.03 ms for ^3F4 → ^3H6 transition, and the integrated emission cross section is 5.81×10^-18 cm^2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm：LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuouswave maximum output power of 0.67 W. The emission wavelengths of Tm：LSO laser are centred around 2.06μm with spectral bandwidth of -13.6 nm.     

Cr（V）与H2络合物的EPR信号

Cr交换丝光沸石在氢气氛中强烈还原并冷却后,出现了一个各向同性的EPR信号,g值2.003,△H_PP 13.4 gauss.采用EHMO方法计算了各种可能模型化合物的g值,结果建议这一信号对应Cr(V)与H₂分子形成的络合物。     

Effects of the strain relaxation of an AlGaN barrier layer induced by various cap layers on the transport properties in AlGaN/GaN heterostructures

The strain relaxation of an AlGaN barrier layer may be influenced by a thin cap layer above, and affects the transport properties of AlGaN/GaN heterostructures. Compared with the slight strain relaxation found in AlGaN barrier layer without cap layer, it is found that a thin cap layer can induce considerable changes of strain state in the AlGaN barrier layer. The degree of relaxation of the AlGaN layer significantly influences the transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. It is observed that electron mobility decreases with the increasing degree of relaxation of the AlGaN barrier, which is believed to be the main cause of the deterioration of crystalline quality and morphology on the AlGaN/GaN interface. On the other hand, both GaN and AlN cap layers lead to a decrease in 2DEG density. The reduction of 2DEG caused by the GaN cap layer may be attributed to the additional negative polarization charges formed at the interface between GaN and AlGaN, while the reduction of the piezoelectric effect in the AlGaN layer results in the decrease of 2DEG density in the case of AlN cap layer.