在β-NaGdF_4∶Tb~(3+)纳米晶中~5D_3→~5D_4的多声子弛豫与局域态密度

实验研究了从体材料到纳米晶(NCs)系统中涉及大能隙(5 800 cm-1)的多声子弛豫(MR)。在MR非线性理论框架下,用单频近似声子谱分析了β-Na Gd F4∶Tb3+NCs中Tb3+:5D3→5D4的MR速率与温度的关系。在12~312 K范围内,实验数据与理论曲线符合得很好。结果表明,MR的产生主要是能量较大的光学声子起作用。在Rayleigh极限下,假设Tb3+发射体位于一个纳米球的中心,使用Green张量方法计算了自发衰减速率Гrad。在纳米球内没有发现局域态密度(LDOS)的明显改变。然而,当R35 nm时,在Chew理论的基础上获得在球外LDOS的一个新的高斯分布。     

离子交换法纯化重组类人胶原蛋白Ⅱ的吸附动力学研究

为了确定重组类人胶原蛋白Ⅱ(Recombinant human-like collagen,RHLC Ⅱ)在CM52树脂上的动力学行为,考察温度、初始浓度等因素的影响,分别采用简单线性推动力模型(液膜扩散控制时)和均相扩散模型(颗粒扩散控制时)研究RHLC Ⅱ在不同工艺条件下的反应速率,确定离子交换过程的速率控制步骤,并计算模型参数.结果表明,(1)速率控制机理受转速和料液初始浓度的影响,在转速和料液初始浓度较低时,为液膜扩散控制(Film Diffusion Control,FDC);反之,则为颗粒扩散控制(Particle Diffusion Control,PDC);(2)以简单线性推动力模型拟合液膜扩散控制时的动力学数据,其线性关系良好,模型准确度较高;对于颗粒扩散控制的吸附,则以均相扩散模型拟合,求出有效扩散系数,模型较好地描述了CM52对RHLC Ⅱ的PDC吸附.(3)对于FDC,温度越高,溶液浓度越大,搅拌转速越高,外扩散速度常数越大,吸附越快;对于PDC,温度升高,有效扩散系数增大,吸附加快,料液浓度对有效扩散系数的影响不显著.     

Scaling in Rate-Changeable Birth and Death Processes with Random Removals

We propose a monomer birth-death model with random removals, in which an aggregate of size k can produce a new monomer at a time-dependent rate I（t）k or lose one monomer at a rate J（t）k, and with a probability P（t） an aggregate of any size is randomly removed. We then anedytically investigate the kinetic evolution of the model by means of the rate equation. The results show that the scaling behavior of the aggregate size distribution is dependent crucially on the net birth rate I（t） - J（t） as well as the birth rate I（t）. The aggregate size distribution can approach a standard or modified scaling form in some cases, but it may take a scale-free form in other cases. Moreover, the species can survive finally only if either I（t） - J（t） ≥ P（t） or [J（t） ＋ P（t） - I（t）]t ≈ 0 at t ≥ 1; otherwise, it will become extinct.     

Atomic Coherent Trapping and Properties of Trapped Atom

Based on the theory of velocity-selective coherent population trapping, we investigate an atom-laser system where a pair of counterpropagating laser fields interact with a three-level atom. The influence of the parametric condition on the properties of the system such as velocity at which the atom is selected to be trapped, time needed for finishing the coherent trapping process, and possible electromagnetically induced transparency of an altrocold atomic medium, etc., is studied.     

用光学-光学双共振光谱技术研究Cs蒸气中的共振交换碰撞

利用窄带半导体激光器泵浦所有具有相同z分量速度的基态Cs原子至激发态,研究了Cs(6P_3/2, v) +Cs(6S_1/2, v′)→Cs(6S_1/2, v) +Cs(6P_3/2, v′)的共振交换碰撞过程。与泵浦光反向平行的另一单模激光器激发6P_3/2至8S_1/2态,以检测6P_3/2态原子的速度分布,确定激发态原子的热能化效应。通过测量8S_1/2→6P_1/2荧光的尖峰强度与相应的多普勒背景的强度比,得到共振交换碰撞速率系数为k=9.62×10-7 cm3·s-1。证明了在纯碱金属蒸气中,由共振交换机制产生的热能化效应的大小比由速度改变碰撞引起的大3个数量级。     

Influence of intensity on the steady and transient state space—charge fields in photorefractive polymers

We have proven theoretically that there are sublinear,linear and superlinear relations between the response rates and total incident intensity for different cases of traps in photorefractive polymer materials.These relations were observed in inorganic photorefractive crystals many years ago.Also,the steady-state space-charge field is a function of the total incident intensity,which has also been found in inorganic photorefractive crystals.We have measured the relations of the steady-state diffraction efficiency and the response rate with respect to the total incident intensity in the photorefractive composite consisting of the polymer (N-vinylcarbazole) (PVK) doped with 4,4‘-n-pentylcyanobiphenyl (5CB) and C60.The results obtained show that the composite belongs to the case of low trap density.     

CFD Simulation of a Hydrogen／Argon Plasma Jet Reactor for Coal Pyrolysis

A Computational Fluid Dynamics (CFD) model was formulated for DC arc hydrogen/argon plasma jet re-actors used in the process of the thermal H2/Ar plasma pyrolysis of coal to acetylene. In this model, fluid flow, convective heat transfer and conjugate heat conductivity are considered simultaneously. The error caused by estimating the inner-wall temperature of a reactor is avoided. The thermodynamic and transport properties of the hydrogen/argon mixture plasma system, which are usually expressed by a set of discrete da-ta, are fitted into expressions that can be easily implemented in the program. The effects of the turbulence are modeled by two standard k-ε equations. The temperature field and velocity field in the plasma jet reactor were calculated by employing SIMPLEST algorithm. The knowledge and insight obtained are useful for the design improvement and scale-up of plasma reactors.     

透射Vop光谱椭圆法对电极附近液层中传质现象的研究

通常的电化学研究中,有关电极附近液层参与反应粒子的传质过程多局限于理论分析,其实验研究,即使应用Fick定律分析液相的扩散传质现象,也多限于简单的均态体系.对于复杂多相体系的液相传质问题,更近乎束手无策.鉴于液相传质研究在理论上和实际应用中的重要性,作者等近年采用透射Vop光谱椭圆法对电化学体系中的传质过程进行了实验探索,本文扼要介绍该法的研究概况.     

反相高效液相色谱法制备洋川芎内酯Ⅰ

建立了一种快速、高效制备洋川芎内酯Ⅰ的工艺路线。以醋酸铵为改性剂,利用台阶梯度洗脱和MCI树脂柱脱盐的方式,通过反相高效液相色谱法制备,从川芎的95%(体积分数)乙醇提取物中快速分离到目标产物洋川芎内酯Ⅰ和副产物阿魏酸。经检测,二者的纯度均达到98%以上。该方法操作简便,能够排除由样品中阿魏酸所引起的峰交叉干扰,上样量大,适合于洋川芎内酯Ⅰ的大量制备。