非等时变分与拉格朗日方程

在理论力学的教学中，基于最小作用量原理推导拉格朗日方程的时候，一般假设了等时变分的条件.本文在非等时变分的条件下重新推导了拉格朗日方程，并解释了非等时变分的物理含义.     

Elastic Scattering of 6He + p at 82.3MeV/nucleon

Differential cross sections for the elastic scattering of halo nucleus 6He on proton target were measured at 82.3 MeV/u. The experimental results axe well reproduced by optical model calculations using global potential KD02 with a reduction of the depth of real volume part by a factor of 0.7. A systematic analysis shows that this behavior might be related to the weakly bound property of unstable nuclei.     

联合体驱使生长法制备ZnO纳米棒及其表征

在常压环境下采用联合体驱使生长(Aggregation-driven growth)法在镀有ZnO纳米薄膜的医用盖玻片衬底和锌箔上制备了不同直径、高取向、密集生长的ZnO纳米棒阵列结构,发现平均直径与生长时间呈线性关系。X射线衍射(XRD)谱图中出现了较强的(002)峰,表明制备的纳米棒阵列具有高度c轴择优生长取向;高分辨透射电子显微镜(HRTEM)和选区电子花样衍射图谱(SAED)结果表明我们得到的单根纳米棒为沿(002)生长的单晶结构。分析确定盖玻片上的纳米棒阵列是以ZnO纳米薄膜缓冲层上的ZnO种子颗粒为成核点生长形成的。     

HIRFL-CSR系统中RIBLLⅡ上中子墙设计的模拟计算

HIRFL-CSR系统中RIBLLⅡ外靶实验终端上的中子探测装置是用来开展放射性束物理以及利用放射性束开展非对称核物质性质等研究的一个重要的探测装置. 介绍了在RIBLLⅡ上计划建造的中子墙的探测原理以及基于Geant4对其所进行的蒙特卡罗模拟, 给出了中子墙的设计方案、优化的设计参数以及中子探测的性能指标.     

Configuration of the valence neutrons of 17B

The reaction cross section of ¹⁷B on ¹²C target at (43.7±2.4)MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (R_rms) was deduced to be (2.92±0.10)fm, while the R_rms of the core and the valence neutron distribution are 2.28fm and 5.98fm respectively. Assuming a ``core plus 2n' structure in ¹⁷B, the mixed configuration of (2s_1/2) and (1d_5/2) of the valence neutrons is studied and the     

丰中子核8He在Si靶上的反应总截面的测量

利用HIRFL 50MeV/u ¹³C束流在Be靶上碎裂,RIBLL选择出丰中子放射性次级束流⁸He,实验测量了25—40MeV/u ⁸He在²⁸Si靶上的反应总截面.采用双参数HO密度分布形式,通过微观Glauber模型拟合⁸He实验数据,发现⁸He具有扩展的中子密度分布.实验结果与Warner反应总截面实验和Alkhazov弹性散射实验结果较好地符合.     

丰中子核6He在28Si靶上的反应总截面测量

实验测量了20—40MeV u的轻丰中子核6He在Si靶上的反应总截面,并且结合6He的高能实验数据,采用双参数HO密度分布形式用Glauber模型计算得到较好的拟合.与Warner的实验数据比较,反应总截面数据系统性好,并与能量有明显的依赖关系. Total reaction cross section (σt) was measured for neuton rich nuclei 6He on 28Si target from about 20 to 40 MeV/u and compared with Warner s experimental data. It is found that the total cross section of 6He on 28Si depends on the energy and it can be fitted well by Glauber model using two term HO density distribution from high energy data of 6He.     

吡啶基有机碱催化O-羧基酐的活性开环聚合

O-羧基酐(OCA)是α-羟基酸与三光气的缩合产物, 其侧基结构丰富, 可开环聚合生成结构多样的聚α-羟基酸, 弥补了聚乳酸结构和性能单一的缺陷. 在OCA开环聚合过程中, 手性α-H容易发生外消旋化, 导致聚合物的立构规整度下降. 本文发现了一种结构简单的高性能有机催化剂—4-甲氧基吡啶, 其可在温和的条件下快速催化OCA的活性开环聚合, 有效抑制酯交换和手性α-H的外消旋化副反应, 合成出高立构规整度的窄分布聚α-羟基酸. 进一步研究发现, 虽然在甲苯和四氢呋喃等常见溶剂中, OCA的开环聚合遵循一级动力学, 但在环氧烷烃溶剂中, OCA开环聚合遵循零级动力学, 聚合反应速率与单体浓度无关. 作为新型高效有机碱催化剂, 4-甲氧基吡啶在多嵌段可降解聚酯高效合成和聚酯生物医药载体制备等方面具有潜在的应用价值.     

Combined multi-level quantum mechanics theories and molecular mechanics study of water-induced transition state of OH~- + CO_2 reaction in aqueous solution

The presence of a solvent interacting with a system brings about qualitative changes from the corresponding gasphase reactions. A solvent can not only change the energetics along the reaction pathway, but also radically alter the reaction mechanism. Here, we investigated the water-induced transition state of the OH~- + CO_2→ HCO_3~- reaction using a multi-level quantum mechanics and molecular mechanics method with an explicit water model. The solvent energy contribution along the reaction pathway has a maximum value which induces the highest energy point on the potential of mean force. The charge transfer from OH~- to CO_2 results in the breaking of the OH~- solvation shell and the forming of the CO_2 solvation shell. The loss of hydrogen bonds in the OH~-solvation shell without being compensated by the formation of hydrogen bonds in the CO_2 solvation shell induces the transition state in the aqueous solution. The calculated free energy reaction barrier at the CCSD(T)/MM level of theory, 11.8 kcal/mol, agrees very well with the experimental value, 12.1 kcal/mol.     

Efficiency calibration of neutron detector array for β decay of exotic nuclei

The research of the in-beam efficiency calibration of Neutron Detector Array of Peking University using ¹⁷N and ¹⁶C beams was introduced in this paper. The efficiency of neutron wall and ball are comparable to the foreign similar devices and neutrons can be detected from low to high energies in high efficiency.