Nd3+:Gd3Sc2Al3O12 晶场能级及拟合

Nd³⁺ :GSAG是性能优良的942 nm激光晶体.用提拉法成功生长Nd³⁺ :GSAG单晶,研究其室温透射光谱,辨认位置高达29967 cm^-1的68个Nd³⁺晶场能级.对这些能级拟合了自由离子及晶场Hamilton参量,拟合标准偏差为16.7 cm^-1,表明实验与计算能级符合很好.获得的Hamilton参量可用于计算Nd³⁺ :GSAG中Nd³⁺的     

(2+1)维孤子系统的多孤子解和分形结构

利用投射方程法和变量分离法,得到了(2+1)维非对称Nizhnik-Novikov-Veselov系统的新显式精确解.根据得到的孤波解,构造出了该系统的多孤子和分形孤子.     

用Excel研究单摆测重力加速度实验中的随机误差分布规律

在单摆法测重力加速度实验中,为了能够快速且正确地得到摆球运动周期的随机误差分布规律,本文提出了一种应用Excel软件给出随机误差统计直方图的方法。该方法简单直观,能够加深同学对随机误差统计规律的认识。     

S波段低温低噪声放大器的研制

介绍了基于ADS仿真的低噪声放大器的设计与制作方法;重点研究了LNA的直流偏置、稳定性分析、匹配设计、版图制作和调试;提出了源级负反馈和栅极加并联阻抗的方法来实现了电路全频段稳定和低温正常工作。采用ATF-34143制作了中心频率在2.25的低噪声放大器,在77K温度下,该放大器带内输入输出驻波比小于1.2,增益达到23dB,噪声系数为0.24dB。     

甲基紫分子拉曼激发虚态的研究

从拉曼峰强入手,求得了甲基紫分子的“时间分辨键极化率”,并与第一原理计算的基态电子密度做对比,讨论了该分子的激发拉曼虚态的性质.研究结果表明,该分子的拉曼激发虚态中电子向分子外围以及两环之间的键流动,并且拉曼弛豫后的键极化率分布与基态电子的密度分布相似.通过研究键极化率的弛豫过程,发现连接两环的键上的键极化率弛豫时间较其他键大.这些结果说明了甲基紫这类双环分子拉曼激发虚态的性质,这对于研究拉曼散射的中间态具有一定意义. 关键词： 拉曼峰强 时间分辨键极化率 弛豫特征时间     

Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack

Shielding effect and emission criterion of a screw dislocation near an interfacial blunt crack are dealt with in this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentials and stress fields due to a screw dislocation located near the interfacial blunt crack. The stress intensity factor on the crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of the orientation of the dislocation and the morphology of the blunt crack as well as the material elastic dissimilarity on the shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations can reduce the stress intensity factor of the interfacial blunt crack tip (shielding effect). The shielding effect increases with the increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuth angle. The critical loads at infinity for dislocation emission increases with the increase of emission angle and curvature radius of blunt crack tip, and the most probable angle for screw dislocation emission is zero. The present solutions contain previous results as special cases.     

SiC纳米棒的紫外发光研究

采用聚硅氮烷前驱体在高温常压下热裂解的方法制备了3C-SiC纳米棒,在室温下观察到来自纳米棒的378 nm（33?eV） 强紫外发射. 利用扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜和X射线衍射对样品的形貌和结构进行表征,观察到在该结构中存在类似6H-SiC结构的三层堆垛层错. 利用室温荧光光谱和室温荧光衰减曲线研究了强紫外发射的产生机理,紫外发射来源于3C-SiC纳米棒中的三层堆垛层错的发光. 关键词： 碳化硅 纳米棒 光致发光     

Current-voltage characteristics of individual conducting polymer nanotubes and nanowires

We report the current-voltage (I-V) characteristics of individual polypyrrole nanotubes and poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires in a temperature range from 300 K to 2 K. Considering the complex structures of such quasi-one-dimensional systems with an array of ordered conductive regions separated by disordered barriers, we use the extended fluctuation-induced tunneling (FIT) and thermal excitation model (Kaiser expression) to fit the temperature and electric-field dependent I–V curves. It is found that the I–V data measured at higher temper-atures or higher voltages can be well fitted by the Kaiser expression. However, the low-temperature data around the zero bias clearly deviate from those obtained from this model. The deviation (or zero-bias conductance suppression) could be possibly ascribed to the occurrence of the Coulomb-gap in the density of states near the Femi level and/or the enhancement of electron-electron interaction resulting from nanosize effects, which have been revealed in the previous studies on low-temperature electronic transport in conducting polymer films, pellets and nanostructures. In addition, similar I-V characteristics and deviation are also observed in an isolated K0.27MnO2 nanowire.     

Atomic and electronic structures of montmorillonite in soft rock

Montmorillonite is a kind of clay mineral which often causes large deformation in soft-rock tunnel engineering and thus brings about safety problems in practice. To deal with these engineering safety problems, the physical and chemical properties of montmorillonite should be studied from basic viewpoints. We study the atomic and electronic structures of montmorillonite by using density-functional theory within the local-density approximation (LDA). The results of calculation show that Al--O bond lengths are longer than Si--O bond lengths. It is found that both the valence band maximum (VBM) and the conduction band minimum (CBM) of montmorillonite are at point Γ, and the calculated direct band gap of montmorillonite is 5.35~eV. We show that the chemical bonding between cations and oxygen anions in montmorillonite is mainly ionic, accompanied as well by a minor covalent component. It is pointed out that the VBM and CBM of montmorillonite consist of oxygen 2p and cation s states, respectively. Our calculated results help to understand the chemical and physical properties of montmorillonite, and are expected to be a guide for solving the problem of large deformation of soft-rock tunnels.     

乙醚团簇在纳秒激光场中的多价电离及其电子能量分布的研究

用5ns,1064nm的脉冲Nd:YAG激光,研究了乙醚团簇与纳秒激光的相互作用.在10¹¹ W/cm²量级光强下,观察到价电子完全剥离的O⁶⁺,C⁴⁺,且这些高价离子的强度比值基本不随激光能量而变化.用阻滞电压方法测量了电离过程中溢出电子能量分布,在最大激光能量4.0×10¹¹ W/cm²,溢出电子的平均能量为56eV,最大能量为102eV.实验结果支持了高价离子产生的“多 关键词： 高价离子 电子能量 纳秒激光 乙醚团簇