棒-板电极下缩比气隙辉光放电相似性的仿真研究

建立了棒-板电极下氩气直流放电的流体模型,利用有限元法对几何位形相似的两个气隙放电过程进行了数值求解.两放电气隙外加电压相同,气隙线性尺寸的比值为10:1,气压分别为1 Torr和10 Torr.仿真得到了两相似气隙的放电的伏安特性曲线以及放电物理量(如电位、电场、电子密度、离子密度、电子温度等)的空间分布.根据气体放电相似性的基本结论,检验了气隙对应物理量之间的数值关系.结果表明:两相似气隙的放电类型为正常辉光放电,对应放电物理量之间存在相似性理论指出的比例关系,且在相同幅值的直流电压作用下,气隙放电的工作点相同.这将为利用气体放电相似性来外推相似气隙的放电特性提供一定的理论依据.     

脉冲激光辐照可见光面阵CCD的入瞳衍射效应

采用波长为532nm的脉冲激光从31.5m的距离辐照可见光面阵电荷耦合器件(CCD),实验观察到了规律性圆环条纹的产生。通过增大激光束的入射角度、调节衰减倍率、重复频率和作用距离,研究了这些规律性圆环条纹的产生条件和机理。结果发现:保持激光器与CCD的作用距离31.5m不变,在激光束的入射角小于或者稍稍大于光学系统半视场角6.8°的情况下,只要光学系统入瞳处的功率密度达到10-3 W/cm2量级,就可以观察到规律性的圆环条纹。通过对探测器表面能量分布进行数学仿真,证实规律性的圆环条纹是由于光学系统入瞳的衍射效应而产生的。     

二元混合体系Gemini表面活性剂G12-6-12和CTAB相互作用的NMR研究

运用NMR方法探讨了298 K时N,N'-双(十二烷基二甲基)-1,6-己烷溴化铵(G12-6-12)和十六烷基三甲基溴化铵(CTAB)在D₂O溶液中的相互作用. 测得G12-6-12和CTAB的临界胶束浓度cmc值分别约为0.773和0.668 mmol/L. 在不同G12-6-12摩尔分数下,混合体系的临界胶束浓度实验值cmc_*小于理想值CMC^*,相互作用参数β_M<0,但是当α≤0.3时,cmc^*比CMC^*小很多,同时 满足|β_M|>ln(cmc₁/cmc₂)条件. 表明G12-6-12和CTAB之间存在协同效应,可以形成混合胶束,在2D NOESY谱中可以看到G12-6-12与CTAB分子间的交叉峰,扩散实验也表明混合溶液中的胶束半径比纯溶液中的G12-6-12胶束半径大,都预示混合胶束的形成. 当α>0.3 时,cmc^*≈CMC^*,β_M≈0, 根据假相分离模型和规则溶液理论,G12-6-12和CTAB近似于理想混合.     

Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction

Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions.     

Open-plus-closed-loop control for chaotic motion of 3D rigid pendulum

An open-plus-closed-loop （OPCL） control problem for the chaotic motion of a 3D rigid pendulum subjected to a constant gravitationM force is studied. The 3D rigid pendulum is assumed to be consist of a rigid body supported by a fixed and frictionless pivot with three rotational degrees. In order to avoid the singular phenomenon of Euler＇s angular velocity equation, the quaternion kinematic equation is used to describe the motion of the 3D rigid pendulum. An OPCL controller for chaotic motion of a 3D rigid pendulum at equilibrium position is designed. This OPCL controller contains two parts： the open-loop part to construct an ideal trajectory and the closed-loop part to stabilize the 3D rigid pendulum. Simulation results show that the controller is effective and efficient.     

新型含哒嗪酮基双酰肼类化合物的3D-QSAR研究

用比较分子场分析方法对1-芳基-1，4-二氢-3-酰肼羰基-6-甲基-4-哒嗪酮类化合物进行了三维定量构效关系研究，发现影响其促进黄瓜子叶生根活性的主要为立体能.立体能与静电能之比为0.733:0.267.所得到的模型交叉验证值rCV2=0.643，相关系数r2=0.977, F=102.622, s=0.041，表明模型具有较好的预测能力.研究结果对3-酰肼羰基-4-哒嗪酮类化合物的改性或新类似物的合成具有指导意义.     

无序碳单层的电子结构及氢原子吸附的第一性原理

本研究运用第一性原理计算方法,系统地研究了无序碳单层材料不同位点的电子结构及其析氢性能.计算结果显示无序结构中的C-C键相比于石墨烯中的C-C键在26.7%的范围内有不同程度的拉伸或压缩,使得C原子电荷在-0.17～+0.16个电子范围内变化,导致部分C原子电子局域化.电子的局域化增强了C原子的化学活性,从而表现出了较强的吸附性能.我们发现H原子与C原子的键合及析氢性能与C原子间的键角相关.对于三配位的碳原子,其中三个价电子通过sp~2杂化轨道与最邻近的碳原子结合形成较强的共价键,而余下的一个p_z轨道电子可以与H原子在垂直于原子层的方向形成较弱的化学键.无序结构可以打破三个sp~2杂化轨道的对称性,进而影响p_z轨道与氢的成键.本研究在一定程度上揭示了单层无序碳材料结构-性能的构效关系,为实验上设计特定性能的无序碳功能材料提供理论指导.     

碳化硅中点缺陷对热传导性能影响的分子动力学研究

碳化硅(SiC)由于性能优异,已广泛应用于核技术领域.在辐照环境下,载能入射粒子可使材料中的原子偏离晶体格点位置,进而产生过饱和的空位、间隙原子、错位原子等点缺陷,这些缺陷将改变材料的热物性能,劣化材料的服役性能.因此,本文利用平衡分子动力学方法(Green-Kubo方法)采用Tersoff型势函数研究了点缺陷对立方碳化硅(β-SiC或3C-SiC)热传导性能的影响规律.研究过程中考虑的点缺陷包括:Si间隙原子(Si_Ⅰ)、Si空位(Si_Ⅴ)、Si错位原子(Si_C)、C间隙原子(C_Ⅰ)、C空位(C_Ⅴ)和C错位原子(C_Si).研究结果表明,热导率(λ)随点缺陷浓度(c)的增加而减小.在研究的点缺陷浓度范围(点缺陷与格点的比例范围为0.2%—1.6%),额外热阻率(Δ_R-R_defect-R_perfect,R=1/λ,R_defect为含缺陷材料的热阻率,R_perfec...     

Magnetic polaron-related optical properties in Ni(Ⅱ)-doped Cd S nanobelts: Implication for spin nanophotonic devices

Emissions by magnetic polarons and spin-coupled d-d transitions in diluted magnetic semiconductors(DMSs)have become a popular research field due to their unusual optical behaviors.In this work,high-quality NiI₂(Ⅱ)-doped CdS nanobelts are synthesized via chemical vapor deposition(CVD),and then characterized by scanning electron microscopy(SEM),x-ray diffraction,x-ray photoelectron spectroscopy(XPS),and Raman scattering.At low temperatures,the photoluminescence(PL)spectra of the Ni-doped nanobelts demonstrate three peaks near the band edge:the free exciton(FX)peak,the exciton magnetic polaron(EMP)peak out of ferromagnetically coupled spins coupled with FXs,and a small higher-energy peak from the interaction of antiferromagnetic coupled Ni pairs and FXs,called antiferromagnetic magnetic polarons(AMPs).With a higher Ni doping concentration,in addition to the d-d transitions of single Ni ions at 620 nm and 760 nm,two other PL peaks appear at 530 nm and 685 nm,attributed to another EMP emission and the d-d transitions of the antiferromagnetic coupled Ni²⁺-Ni²⁺pair,respectively.Furthermore,single-mode lasing at the first EMP is excited by a femtosecond laser pulse,proving a coherent bosonic lasing of the EMP condensate out of complicated states.These results show that the coupled spins play an important role in forming magnetic polaron and implementing related optical responses.     

Systematic study on α-decay half-lives of uranium isotopes with a screened electrostatic barrier

In the present work, we systematically study the α-decay half-lives of uranium (Z=92) isotopes based on the Gamow model with a screened electrostatic barrier. There are only two adjustable parameters in our model i.e. the parameter g and the screening parameter t in the Hulthen potential for considering the screened electrostatic effect of the Coulomb potential. The calculated results are in good agreement with experimental data, and the corresponding root-mean-square (rms) deviations of uranium isotopes with α transition orbital angular momentum l=0 and l=2 are 0.141 and 0.340, respectively. Moreover, we extend this model to predict α-decay half-lives of uranium isotopes whose α decay is energetically allowed or observed but not yet quantified in NUBASE2020. For comparison, the modified Hatsukawa formula (XLZ), the unified Royer formula (DZR), the universal decay law (UDL) and the Viola–Seaborg–Sobiczewski formula (VSS) are also used. The predictions are basically consistent with each other. Meanwhile, the results also indicate that N=126 shell closure is still robust at Z=92 and the spectroscopic factor \begin{document}$ S_{\alpha} $\end{document} is almost the same for uranium isotopes with the same l.