基于点缺陷扩散理论与离散位错动力学耦合的位错攀移模型研究

位错的攀移运动对高温下晶体材料的塑性行为有重要影响,为了能够有效揭示攀移的物理本质及其对塑性行为的作用,本文基于点缺陷扩散理论,通过将体扩散和管扩散机理的共同作用与三维离散位错动力学耦合,建立了适用条件更广的位错攀移模型. 利用此模型我们模拟了单个及多个棱柱型位错环的收缩变形过程,发现影响位错攀移速率的决定因素不是传统理论认为的机械攀移力,而是位错周围(体扩散)及位错段上(管扩散)的空位浓度梯度. 该模型也能够完全重现棱柱型位错环群的粗化过程中不同位错环半径及晶体内平均空位浓度随时间变化的三个阶段. 关键词： 位错攀移 点缺陷扩散理论 位错动力学 棱柱位错环     

MnO_2对TiO_2光催化降解苯胺的影响

采用动力学方法研究了MnO2颗粒物对TiO2光催化降解苯胺活性的影响,对比考察了光催化降解过程中苯胺溶液的UV吸收光谱的变化,并用HPLC方法鉴别了中间产物.结果表明,少量MnO2颗粒物就能使TiO2光催化降解苯胺的活性受到明显的抑制,不同结构的二氧化锰致毒效应由大到小的顺序为:δ-MnO2α-MnO2β-MnO2;降解不同时间后溶液的UV吸收光谱的变化也反映了MnO2颗粒物具有同样的致毒效应;MnO2颗粒物不改变TiO2光催化降解苯胺的途径,但对生成中间产物的基元步骤的抑制程度不同。     

光催化技术简介

介绍了光催化反应原理,光催化剂TiO2的晶体结构,以及光催化技术存在的主要问题,如量子产率偏低、光谱响应范围窄、催化剂分离和回收难、高浓度废水透光率低、光催化剂失活等,并简要分析了光催化剂的研究现状。     

Marcinkiewicz 空间中带可变指数的熵解的先验估计

本文研究p(x)-Laplace方程的退化形式的带可变指数的Dirichlet问题,得到了Marcinkiewicz空间中带可变指数的熵解的先验估计.     

Reaching a few 10~(-15) long-term stability of integrating sphere cold atom clock

We present the long-term stability of the integrating sphere cold atom clock(ISCAC) and analyze its systematic limitations. The relative frequency instability of 2.6 × 10~(-15) is reached for an averaging time of 2 ×10~5 s. The second-order Zeeman effect and the cavity pulling effect in ISCAC, which would induce the frequency drift from the clock transition, are analyzed. The analytical and experimental results indicate that the cavity pulling effect is the main contribution to the long-term frequency instability of the ISCAC. Further technical improvements to the microwave cavity are also discussed.     

N-乙酰葡萄糖胺的性质、制备及用途

介绍N-乙酰葡萄糖胺的性质、制备和用途,尤其是在医学上的用途。     

Muon radiography technology for detecting high-Z materials

This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA （Point of Closest Approach） algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.     

Synthesis and properties of Au-Fe3O4 and Ag-FeaO4 heterodimeric nanoparticles

Monodisperse Au-Fe3O4 heterodimeric nanoparticles （NPs） were prepared by injecting precursors into a hot reaction solution. The size of Au and Fe3O4 particles can be controlled by changing the injection temperature. UVis spectra show that the surface plasma resonance band of Au-Fe3O4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size. The as-prepared heterodimeric Au-Fe3O4 NPs exhibited superparamagnetic properties at room temperature. The Ag-Fe3O4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO3 as precursor instead of HAuCl4. It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.     

High-order harmonic generation with a two-color laser pulse

We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field. We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays. We find that the width of the harmonic plateau can be extended when the control electric field is added, and a supercontinuum from 198 to 435 eV is generated, from which an isolated 61-as pulse can be directly obtained.     

频域有限元计算的扩展面向目标误差估计

研究了针对频域有限元直接动态分析的面向目标误差估计以及误差范围估计计算方法．面向目标的误差估计方法就是专门针对如何准确和经济地估算特定值误差的一种方法,利用原问题的共轭偶问题进行计算．频域有限元的直接动态分析是模拟频域扫描实验的一种计算方法,专门针对谐振激励的线性动态响应问题,利用将原自由度分解为实部和虚部描述频率的变化,从而计算变形体的动态响应．利用扩展针对有限元的面向目标误差估计的自由度,将该方法应用到直接动态分析中进行误差估计．通过建立同时包含实部和虚部自由度的能量弱形式及偶问题,并将其数值实现,估算频域直接动态分析有限元解的误差及误差范围,并通过悬臂梁的激振算例进行了验证．