Strong reaction channels at barrier energies in the system 6Li + 208Pb

Large cross-section reaction channels were measured in the systems ⁶Li( ⁷Li) + ²⁰⁸Pb with high statistical accuracy at 5(3) energies around the Coulomb barrier from 29 to 39 MeV. These channels were assigned (mainly) to the breakup of ⁶Li, very loosely bound, into α + d and to the breakup of ⁵Li, produced by n-transfer to the target, into α + p and to similar processes with ⁷Li beam. The cross-sections with ⁶Li, S _α = 1.475 MeV, are systematically larger than the ⁷Li ones. This reflects, most likely, the higher binding energy of ⁷Li, S _α = 2.468 MeV. Theoretical predictions for the ⁶Li + ²⁰⁸Pb system which include for ⁶Li breakup to continuum states within a continuum discretized coupled-channels approach (CDCC) and resonant breakup plus n-transfer with DWBA reproduce the angular distribution shapes but still underestimate the cross-sections by a factor ∼ 3. Received: 15 January 2001 / Accepted: 3 March 2001     

增殖剂球床载气体流动特性

增殖剂球床是聚变堆或混合堆产氚包层可选结构之一,准确把握增殖剂球床中载带气体的流动特性有助于提高对球床载氚过程的认识并优化包层设计。采用离散元程序PFC3D模拟增殖剂小球的填充行为,在球床内不同位置随机截取不同尺寸的控制体,利用布尔运算中的"差集"得到孔隙范围,建立孔隙分布的三维几何模型,进一步划分网格并用计算流体力学(CFD)方法求解,得出控制体上单位长度的压降以及单元体内的速度分布特征,计算结果发现载带气体速度分布与γ分布很类似,且只要选取恰当的控制体,通过计算流体力学方法可以较好地分析整个球床孔隙内流体的流动,有利于进一步研究载氚及相关过程。     

FeTe合金结构分析及其薄膜制备

利用固态反应法制备了名义成分为FeTe的合金, 采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其相组成和晶体结构. 研究表明,主相为Fe_1.08Te,空间群为P4/nmm,点阵参数 a = 3.8214(3) Å, c = 6.2875(3) Å, Z = 2, Fe原子占据2a和2c晶位, Te原子占据2c晶位. 利用脉冲激光沉积技术制备的FeTe薄膜超导转变起始温度为13.2 K,零电阻温度为9.8 K. 关键词： FeTe Rietveld结构精修 超导薄膜     

Effects of substrate temperature upon the properties of ZnMgTe layer grown by MOVPE

The effects of substrate temperature upon the optical property, composition and surface morphology have been investigated on nominally undoped Zn_1−xMg_xTe layers grown on (1 0 0) ZnTe substrates by atmospheric pressure metal organic vapor phase epitaxy (MOVPE). It was found that Mg composition increases with decreasing substrate temperature. The result of low temperature photoluminescence (PL) measurement suggests that the optical quality of Zn_1−xMg_xTe layers becomes better with decreasing substrate temperature. On the other hand, there is a narrow range of optimal substrate temperature for a smooth surface morphology. For all the layers, a two-mode behavior with ZnTe- and MgTe-like longitudinal optical phonon modes was confirmed by Raman scattering.     

Energy transfer between activators at different crystallographic sites in Sr3SiO5:Eu

A yellow phosphor, Sr₃SiO₅:Eu²⁺, was synthesized by a high temperature solid-state method. Sr₃SiO₅:Eu²⁺ exhibits a single yellow emission under the blue radiation excitation. However, Sr₃SiO₅:Eu²⁺ shows a two-peak emission under the ultraviolet radiation excitation when Eu²⁺ doping content is less than 0.01 mol. Moreover, the blue emission disappears and the yellow emission reaches the peak value when Eu²⁺ doping content is 0.01 mol. Namely, the energy transfer takes place between the Eu²⁺ activators, which is located at two different crystallographic sites in the Sr₃SiO₅. And the energy transfer mechanism is the dipole-dipole interaction.     

一种近红外光谱在线监测新方法及其在中药柱层析过程中的应用

近红外光谱(NIRS)广泛应用于生产过程分析与监测,常需事先建立定量校正或定性判别模型,并需在生产条件变化后调整模型,使用较复杂。本文从相异度和相似度两个对立互补的角度,提出自适应移动窗口标准差法和过程光谱相似度法,并以此为基础建立一种针对生产过程的无需校正模型的简易光谱在线监测方法。论文以中药柱层析过程为例,对监测过程作NIRS自适应移动窗口标准差趋势图和过程光谱相似度趋势图,并通过HPLC离线分析所得的多指标成分含量变化趋势图进行对比验证,发现可用于工艺状况实时监测,指导收集起点、终点、溶液相变点的判断,表明论文提出的方法合理可行。该方法亦可用于紫外/可见、红外、拉曼、荧光等光谱及色谱、质谱等其他过程分析技术。     

First-principles investigation on the elastic stability and thermodynamic properties of Ti2SC

Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation（GGA） in the frame of density functional theory（DFT）,we have investigated the crystal structures,elastic,and thermodynamic properties for Ti2SC under high temperature and high pressure.The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results.The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures.The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa.Investigations on the elastic properties show that the c axis is stiffer than the a axis,which is consistent with the larger longitudinal elastic constants（C 33,C 11） relative to transverse ones（C 44,C 12,C 13）.Study on Poisson＇s ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure.The ratio（B/G） of bulk（B） and shear（G） moduli as well as B/C 44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure.Moreover,the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures.Again,we observed that the Debye temperature and Gru篓neisen parameter show weak temperature dependence relative to the thermal expansion coefficient,entropy,and heat capacity,from which the pressure effects are clearly seen.     

Luminescence of a GaN grain with a nonpolar and semipolar plane in relation to microstructural characterization

We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask.Transmission electron microscopy,scanning electron microscopy,and Raman spectroscopy are used to reveal the effect of SiN on the overgrown a-plane GaN growth.The SiN layer effectively terminates the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN regrowth through the interlayer,resulting in the window region shrinking from a rectangle to a "black hole".Furthermore,strong yellow luminescence(YL) in the nonpolar plane and very weak YL in the semipolar plane on the GaN grain is revealed by cathodoluminescence,suggesting that C-involved defects are responsible for the YL.     

Density functional study of TaSin (n = 1-3, 12) clusters adsorbed to graphene surface

A plane-wave density functional theory (DFT) calculations have been performed to investigate structural and electronic properties of TaSi_n (n = 1-3, 12) clusters supported by graphene surface. The resulting adsorption structures are described and discussed in terms of stability, bonding, and electron transfer between the cluster and the graphene. The TaSi_n clusters on graphene surface favor their free-standing ground-state structures. Especially in the cases of the linear TaSi₂ and the planar TaSi₃, the graphene surface may catalyze the transition of the TaSi_n clusters from an isomer of lower dimensionality into the ground-state structure. The adsorption site and configuration of TaSi_n on graphene surface are dominated by the interaction between Ta atom and graphene. Ta atom prefers to adsorb on the hollow site of graphene, and Si atoms tend to locate on the bridge site. Further, the electron transfer is found to proceed from the cluster to the surface for n = 1 and 2, while its direction reverses as n > 2. For the case of TaSi, chemisorption is shown to prevail over physisorption as the dominant mode of surface-adsorbate interaction by charge density analysis.     

基于小波变换和高斯拟合的在线谱图综合处理方法

微小型移动式现场在线检测技术是分析仪器发展的新领域。针对复杂工作环境中谱图存在强噪声干扰、谱峰重叠、不规则峰形等严重影响仪器的定性和定量准确度的瓶颈技术,提出了一种基于小波变换和高斯拟合相结合的谱图在线综合处理方法,用自研的仪器对甲苯和全氟三丁胺两种典型化合物的谱图进行了处理,并与实验室分析仪器普遍应用的算法进行了对比分析。结果表明,综合方法能够有效解决强噪声干扰、谱峰重叠、不规则峰形问题,提高仪器的定性和定量准确性,同时能够实现数据压缩,满足仪器的在线实时检测要求。综合方法处理甲苯特征峰的平均信噪比(SNR)较移动平滑方法提高了1.3倍,峰位误差ΔM降低了3.6倍,处理全氟三丁胺谱图的数据压缩比为197∶1。