三能级体系的Z回波核磁共振粉末谱

本文提出一个Z回波核磁共振(NMR)脉冲序列,可以获得三能级体系的纯偶极或纯四极谱。Z回波NMR谱不仅与化学位移各向异性无关,而且在强射频场条件下,与射频场非均匀性无关。该方法明显优于章动NMR技术。以上结论经过理论分析和实验结果的验证。 关键词：     

优化重聚脉冲提高梯度场核磁共振信号强度

缩短射频脉冲宽度, 有助于解决脉冲电力消耗大、样品吸收率高、信噪比低等极端条件核磁共振探测的关键问题. 本文首先分析射频脉冲角度对核磁共振自旋回波信号强度的影响机理, 基于Bloch方程推导了回波信号幅度与扳转角、重聚角的关系. 在特制核磁共振分析仪上采用变脉冲角度技术, 分别在均匀磁场和梯度磁场条件下实现对扳转角和重聚角与回波信号强度关系的数值模拟和实验测量. 结果表明, 梯度场中, 扳转角为90°、重聚角为140°的射频脉冲组合获得最大首波信号强度, 比180°脉冲对应的回波幅值提高13%, 能耗降低至78%. 选用该重聚角(140°) 优化设计饱和恢复脉冲序列探测流体的纵向弛豫时间T₁特性, 准确获得 T₁分布.该结果对于低电力供应、且对信噪比有较高要求的核磁共振测量, 如随钻核磁共振测井和在线核磁共振快速检测等, 具有重要意义. 关键词： 核磁共振 信号强度 重聚脉冲角度 Bloch方程     

随机电报过程引起的光失相的计算

本文计算了红宝石中Al核自旋跳变引起的R₁[⁴A₂(S=-3/2)→²E(S=-1/2)]回波衰减。用随机电报过程描述每个Al核自旋(i)跳变引起Cr共振频率的起伏Δi,这个过程对光子回波衰减的贡献〈E_i(t₂₁)〉可以用解析式表示。首先计算核自旋(i)跳变的总速率Wi及它引起的Δi,求出〈E_i(t₂₁)〉。设对Cr光失相起主要贡献的每个Al核自旋跳变近似是独立的,所以总的回波强度是所有Al引起的〈E_i(t)₂₁〉的乘积。计算得到非指数的回波衰减,以I=I₀exp〔-(4t/t_m)^x〕拟合,x=2.56,t_m=50.6μs,与实验及计算机模拟的结果一致.     

氮气射频放电与直流放电PIC/MC模拟的比较

建立氮气容性射频等离子体过程的PIC/MC模型,将模拟结果与直流放电进行比较.结果表明:射频等离子体粒子(e,N₂⁺,N⁺)的平均密度较直流放电约大-个量级,在射频电极附近粒子(e,N₂⁺,N⁺)的平均能量比直流放电阴极附近的能量低3倍左右;密度偏低的原子离子N⁺在两电极附近具较高的能量,能量较低的分子离子N₂⁺在放电空间具较高密度,N₂⁺的密度大约是N⁺的6倍;计算的电子能量几率分布与测量结果-致.     

基于FPGA的低场核磁共振谱仪脉冲编程器设计与实现

脉冲编程器在核磁共振(NMR) 谱仪中非常重要,具有产生脉冲序列所需的射频脉冲,控制回波信号的同步接收等功能. 基于FPGA的同步性能和时序控制功能,设计了低场NMR谱仪的脉冲编程器,可产生任意脉冲序列,实现脉冲频率、相位、幅度的灵活调节. 利用设计的脉冲编程器在0.540 Tesla均匀磁场下进行了CuSO₄溶液的T₁和T₂测量,得到高信噪比的NMR回波串.     

利用超声脉冲回波重合法测定铌酸锂单晶弹性常数CijE和CijD

本文从基本的压电Christoffel方程出发导出三角晶系3m点群压电晶体弹性常数的表示式。并采用10MHz射频超声脉冲回波重合法测量了沿LiNbO₃不同对称方向传播的声速,结合e_ij和ε_ij⁵给出了LiNbO₃全部弹性常数C_ij^E和C_ij^D。它们是C₁₁^E=19.8 关键词：     

自旋回波技术在31P谱中的应用

本文将自旋回波技术用于识别直接与³¹P核偶合(³¹P-¹H)和远程偶合(³¹P-O-C-¹H)的氢类型。例举了二烷基二硫代磷酸、二烷基磷酸酯及其他几种产物中自旋回波方法归属的结果。     

无源射频识别系统中的雷达截面分析与计算

基于无源射频识别技术原理和天线散射理论,导出了不同负载情况下的雷达截面计算方法,并结合雷达截面和电磁传播环境分析了无源射频识别系统的识别距离.通过测量标签天线不同负载情况下的反向散射功率,再结合该计算方法,从而得出雷达截面.理论分析与实验测量结果保持一致.研究结果对优化无源射频识别系统的标签性能有益. 关键词： 射频识别 天线 雷达截面 识别距离     

粉末样品中氘核NMR的回波序列

本文提出一个回波序列,它由四个90和一个45脉冲构成,具有较宽的激发带宽和较短的激发时间,可用于氘核NMR固体线型的测量之中,数值计算结果表明该回波序列的激发带宽几乎比传统的四极回波宽一倍。²D-PMMA粉末样品的实验结果证实了本文设计的回波序列的优越性。     

1-甲基环氧乙烷-1-丙炔醚的结构测定及其核磁图谱

以¹H-NMR谱和¹³C双自旋回波的APT脉冲序列测定文献中尚未曾发表的化合物HC≡C-CH₂-O-C^CH₃-_O-CH₂文中计算了峰强度与脉冲间隔时间的关系,讨论了各谱线的相位并区分出-CH₃、-CH₂、-CH和季碳。     

The K-, L- and M-Auger and L-Coster-Kronig spectra of platinum

The K-, L- and M-Auger and L-Coster-Kronig spectra of platinum in the electron capture decay of ¹⁹⁵Au was measured by means of the Vanderbilt iron-free, double-focussing spectrometer. The energies and relative intensities of 55 peaks were measured in the L-Auger spectrum in the energy range of 5 to 12 keV. The intensities are compared to those calculated theoretically for silver by Asaad. The total L-Coster-Kronig plus M-Auger intensity (0 to 3.25 keV) was measured relative to the L-Auger intensity. The measured relative intensities of the KLL Auger lines are compared to the theoretical and experimental results of others. The measured KLL energies agree with those calculated semi-theoretically by Hörnfeldt and by Listengarten. A value of KLX/KLL = 0.548±0.044 was measured. A measurement of the KL₃L₃(³P₀)/KL₃L₃(³P₀+³P₂) ratio, the first reported in this Z-region, gave a value of 0.095±0.024.     

Electron state in TiO studied by measurements of compton profile and scattering factors

Compton profileswere measured on TiO_1.25 and TiO_0.82 with an SSD and γ-ray source. The results were compared with the profiles calculated from isolated ions and also with the scattering factor values obtained with the critical voltage effect.     

QUANTUM EFFICIENCY AND MULTIPHONON NONRADIATIVE TRANSITION OF Er3+ IONS IN FLUORIDE GLASS

Optical absorption, emission and excitation spectra, lifetimes of ⁴S_3/2 state and ⁴F_9/2 state from 10K to 500K, and Raman spectra were measured for Er³⁺ ions in fluoride glass. The radiative transition probabilities were calculated on the basis of Judd-Ofelt theory. The nonradiative transition probabilities and the quantum efficiencies were determined by calculating the difference between the measured lifetimes and the calculated radiative transition probabilities. The temperature dependence of nonradiative transition provavility was investigated using the Huang-Rhys theory of multiphonon relaxation , in which two kinds of phonons as well as the parameter s were taken into consideration. A fairly good agreement of the theoretical calculation with the experimental results has been obtained. The value of s is estimated and the effect of s is discussed.     

Ce3+,Tb3+共掺BaYF5微晶玻璃的光学特性

采用高温熔融法制备了一种新型的Ce3 +/Tb3+共掺BaYF5微晶玻璃.测试了微晶玻璃的X射线衍射图(XRD)谱、激发光普和发射光谱.研究发现:660℃热处理2h后的玻璃基质中析出BaYF5纳米晶相,根据XRD结果用Scherrer公式计算得到晶粒大小约为27 nm;在近紫外光(338 nm)激发下,观察到BaYF5...     

Al2O3吸附[Cu(H2O)6]2+基团的自旋哈密顿参量和四角畸变

采用微扰方法和对角化完全能量矩阵法计算了Al₂O₃粉末吸附的四角对称[Cu(H₂O)₆]²⁺基团的自旋哈密顿参量（g因子g∥,g_⊥和超精细结构常数A_∥和A_⊥）. 计算结果表明用这两种理论方法计算的自旋哈密顿参量很接近,并且都与实验结果比较一致. 表明这2种方法都可用于晶体中3d9离子基团的自旋哈密顿参量的研究,通过计算,我们还获得了[Cu(H₂O)₆]²⁺基团四角畸变的大小,并对结果进行了讨论.     

Spin fluctuations in weakly itinerant ferromagnets Y(Co1−xAlx)2

The nuclear spin-lattice relaxation rate, 1/T₁, has been measured in weak itinerant ferromagnets Y(Co_1−xAl_x)₂. The temperature and magnetic field dependence of 1/T₁T has been found to be well described by the self-consistent renormalization (SCR) theory of spin fluctuations. The parameters characterizing spin fluctuations in this system were estimated from NMR and magnetic measurements. The temperature dependence of susceptibility calculated from these parameters well reproduces the experimental results.     

通过超宽139La固体核磁共振波谱研究层状La(OH)2NO3

层状稀土氢氧化物是一类新型的稀土功能材料，本文采用固体核磁共振（SSNMR）方法研究了同时具备离子交换能力和非线性光学特性的层状La（OH）₂NO₃化合物，探讨了通过四极核CPMG（QCPMG）脉冲序列和变频谱图采集获取超宽¹³⁹La SSNMR谱图的方法，并描述了适用于此类实验的滤波方程和谱图重建方法.重建谱图同时包含四极核中心跃迁和卫星跃迁信息，本文使用QUEST软件对超宽¹³⁹La NMR谱图进行了模拟，获取的四极耦合常数C_Q和非对称因子η_Q均与CASTEP密度泛函理论计算值高度吻合.SSNMR实验结果证实层状La（OH）₂NO₃化合物属于非中心对称结构（P2₁），解决了对其结构长期以来存在的争论.     

Heat capacity investigation of dopant effects on the magnetic disordering temperature in Fe3O4†

The heat capacities of ZnFe₂O₄, Zn_0.005Fe_2.995O₄, Zn_0.066Fe_2.934O₄, and Cd_0.010Fe_2.990O₄ were measured over the temperature range of 350–1000 K by means of differential scanning calorimetry. The temperatures at which the maximum in heat capacity occurs due to the ferrimagnetic anomaly in the doped-Fe₃O₄ samples were found to decrease with increasing dopant. The excess entropy associated with the ferrimagnetic anomaly was estimated using three methods. One method, used previously for Fe₃O₄, employed a calculated lattice contribution for Fe₃O₄. The other two methods used the experimentally determined heat capacity of ZnFe₂O₄, either unmodified or mass adjusted, to approximate contributions from lattice vibrations.     

快重离子辐照对MoS2热导率的影响研究

利用0.97 GeV的209Bi离子辐照二硫化钼（MoS₂）晶体,辐照注量范围为1×1010～1×1012 ions/cm2,结合原子力显微镜（AFM）观测和Raman光谱分析研究了快重离子辐照对MoS₂热导率的影响。实验结果显示,快重离子辐照在MoS₂中产生了潜径迹,较高激光功率下的Raman测试使样品局部温度升高,导致E_1/2g和A_1g峰随注量增加向低波数方向移动,且峰形展宽。引入了通过改变激光功率测量Raman光谱得到MoS₂热导率的计算方法,获得了不同辐照注量下MoS₂的热导率的定量分析结果,随注量增加,热导率不断降低,从未辐照样品的563 W/mK下降到1×1012 ions/cm2辐照时的132 W/mK。Molybdenum disulphide (MoS₂) was irradiated by 0.97 GeV 209Bi ions with the fluence of 1×1010 to 1×1012 ions/cm2. The irradiation effect on the thermal conductivity of MoS₂ was analyzed by atomic force microscope (AFM) and Raman spectroscopy. The experimental results show that hillock-like latent tracks are observed on irradiated MoS₂ by AFM. The measurement of MoS₂ by Raman spectrometer with high laser power results in the increase of local temperature of MoS₂, which cause the downshift of peaks position and broadening of E_1/2g and A_1g peak. Furthermore, according to Raman spectra measured at different laser power, thermal conductivity of MoS₂ before and after irradiation was calculated, which show that the thermal conductivity of MoS₂ decreases with increasing fluence, from 563 to 132 W/mK for pristine and 1×1012 ions/cm2 irradiated MoS₂, respectively.     

Gd2(WO4)3: Eu纳米发光材料中黄昆因子和能量传递速率的实验获得

采用共沉淀法制备了不同Eu³⁺掺杂浓度的Gd₂(WO₄)₃纳米发光材料. 测量了纳米材料样品的X射线衍射谱(XRD) 和场发射扫描电镜, 对样品的结构和形貌进行了表征. 测量了各样品的发射光谱和激发光谱(声子边带光谱), 绘制了浓度猝灭曲线, 确定了最佳的掺杂浓度为20 mol%. 通过声子边带光谱计算了不同掺杂浓度样品的黄昆因子. 测量了不同浓度样品的荧光寿命, 利用Auzel模型对Eu^{3+ 5}D₀能级荧光寿命数据进行了拟合, 确定了⁵D₀能级的固有寿命和猝灭过程中生成的声子数. 本文还根据荧光寿命数据计算了Eu³⁺之间的能量传递速率, 确定了能量传递速率与浓度的关系. 关键词： 钨酸盐 3+')" href="#">Eu³⁺ 黄昆因子 能量传递速率