晶体LiCl∶Ni2+局域结构、吸收光谱和电子顺磁共振谱的研究

采用半自洽场自由Ni2+的3d轨道模型以及点电荷-偶极子模型,利用完全对角化方法,建立了LiCl∶Ni2+晶体的D2h对称局域结构与吸收光谱、电子顺磁共振谱之间的定量关系,统一解释了LiCl∶Ni2+晶体的局域结构与吸收光谱、电子顺磁共振谱,确定了实验中测得的零场分裂D、E的符号,预测了实验中未测得的LiCl∶Ni2+晶体的精细吸收光谱.理论计算结果与实验观测值符合得很好.     

金刚石荧光机制的研究及其对高压拉曼光谱测试的意义

基于金刚石压腔技术的高压拉曼散射光谱在高压科学的前沿研究中发挥重要作用,金刚石压砧的荧光效应影响测试样品的拉曼散射光谱信噪比。采用激光拉曼光谱仪,对202粒宝石级金刚石进行光致发光研究,确定了N3、H3和NV~0中心等光学缺陷中心的存在,发现其浓度控制零声子线及荧光发射谱的强度,与金刚石荧光强度呈正相关。金刚石的二阶拉曼位移峰(约2664 cm~(–1))两侧基线强度比值与荧光强度呈负相关,利用该比值可准确判断金刚石荧光的强弱。此外,金刚石中光学缺陷中心浓度的不均匀性普遍存在,多点测试综合分析能提供更全面的荧光信息。研究结果可为高压拉曼测试时金刚石压砧的选择提供有效的理论和实践依据。     

Spin Pumping from a Quantum Dot in the Presence of Decoherence

We study the pumped spin current of an interacting quantum dot tunnel coupled to a single lead in the presence of electron spin resonance （ESR） field. The spin decoherence in the dot is included by the Bffttiker approach. Using the nonequilibrium Green＇s function technique, we show that ESR-induced spin flip can generate finite spin current with no charge transport. Both the Coulomb interaction and spin decoherence decrease the amplitude of spin current. The dependence of pumped spin current on the intensity and frequency of ESR field, and the spin decoherence is discussed.     

Temperature Dependence of Photoluminescence from Single and Ensemble InAs/GaAs Quantum Dots

We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier-phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.     

Characterization Method of Polycrystalline Materials Using Conductive Atomic Force Microscopy

An apparatus for characterization of polycrystalline materials based on conductive atomic torce microscopy （cAFM） is developed and a quantitative measurement of electrical characteristics of individual grains in polycrystalline ZnO ceramic is demonstrated. Improvement of the experimental method is presented. Experimental results illuminate unambiguously the different electrical characteristics between individual grains, suggesting the suitability and maneuverability of this method in the study of local structure or properties and their relationship in polycrystalline materials such as semi-conducting ceramics.     

低温透平膨胀机的热力参数计算及数值模拟校核北大核心

针对某液化装置用一级透平膨胀机进行一维热力参数设计计算并使用商业软件ANSYS进行三维数值模拟的校核。计算表明,一维设计所得结果具有一定准确性。三维校核过程中,分别使用理想气体、PR方程以及He Pak三种不同的氦气体工质物性库,三者对工质密度计算的数据存在较大差别,且压力越大差别越大;喷嘴叶片表面压力分布差别较小,温度分布差别较大;工作轮叶片表面压力分布在前缘处有一定差别,尾缘处变化曲线基本重合,温度分布同样差别较大。此次模拟校核表明,理想气体物性库与实际气体物性库的结果存在一定偏差,故对于小型低温透平膨胀机而言,即便温区在20K以上,也应使用实际气体物性库对其进行数值模拟。     

Magnetic properties of misch-metal partially substituted Nd–Fe–B magnets sintered by dual alloy method

The misch-metal(MM) partially substituted Nd–Fe–B sintered magnets were fabricated by the dual alloy method,and the crystal structure, microstructure, and magnetic properties were analyzed comprehensively. X-ray diffraction(XRD)reveals that the increasing content of the MM has an inconsiderable effect on the crystallographic alignment of the magnets.Grains of the two main phases are uniformly distributed, and slightly deteriorate on the grain boundary. Due to the diffusion between the adjacent grains, the MM substituted Nd–Fe–B magnets contain three types of components with different Ce/La concentrations. Moreover, the first-order reversal curve(FORC) diagram is introduced to analyze the magnetization reversal process, coercivity mechanism, and distribution of reversal field in magnetic samples. The analysis indicates that there are two major reversal components, corresponding to the two different main phases. The domain nucleation and growth are determined to be the leading mechanism in controlling the magnetization reversal processes of the magnets sintered by the dual alloy method.     

“海纹石”的矿物学及谱学特征研究

“海纹石”是具有蓝色条带的针钠钙石,是一种稀有的宝石材料,具有较好的市场前景。为查明其矿物学特征及成因,采用常规宝石学测试并结合X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、拉曼光谱(Raman)、扫描电镜(SEM)及紫外-可见分光光度计(UV-Vis)等现代测试方法,对“海纹石”不同颜色部分的矿物成分及特征进行了深入分析。XRD,FTIR,Raman分析结果表明,“海纹石”的主要组成矿物为针钠钙石,并含有少量的方解石,与SEM分析结果较为一致。FTIR分析显示,“海纹石”白色部分在1 500 cm-1处出现一个明显的宽吸收带并伴有883和710 cm-1的吸收峰,表明含有少量方解石,而蓝色部分在该处没有此吸收。紫外可见吸收光谱分析显示蓝色部分在可见光区有640 nm宽吸收峰,表明可能含有微量元素Cu。“海纹石”白色和蓝色部分矿物组分的差异,表明两者可能形成于不同的地质环境。     

基于电子舌技术对不同年份的化橘红的识别

不同年份的化橘红功效和价格均存在差异,为了快速识别未知橘红样品的年份,采用电子舌对2001～2010年的10个样品和一个盲样进行了分析.对原始数据采用主成分分析和判别因子分析.结果表明:主成分分析可以将不同年份的样品进行有效的区分,判别因子分析可以更好地区分不同年份的样品,并能进行盲样识别.在模式识别中,判别因子分析法的识别结果均优于主成分分析法,前者2个判别因子的累计方差贡献量达到了99.929%.电子舌可以较好地区分不同年份的化橘红,改进后有望应用于化橘红的快速检测.     

α-蒎烯/β-蒎烯共聚物合成与表征

α-蒎烯/β-蒎烯共聚物合成与表征;松节油;α-蒎烯;萜烯树脂;阳离子聚合