当能级间隔较小时三能级核四极共振自旋系统对脉冲的响应

用虚拟自旋—１／２算符理论考察了Ｉ＝１的核四极共振自旋系统在其能级间隔较小时对１—２个脉冲的响应．由于核四极相互作用表象中的射频场与核自旋的相互作用（Ｈｎ）包含时间．因而用Ｄｙｓｏｎ时序算符来计算密度算符在Ｈｎ作用下的演化．     

自旋I=3/2核四极共振体系对梳状脉冲的响应

用密度矩阵理论和计算机模拟较详细地讨论了自旋I=3/2核四极共振(NQR)粉末体系对梳状脉冲的响应以及偏共振效应的影响.在偏共振强度(包括谱线的非均匀增宽)较小的条件下.由它获得的谱与二维章动谱是相似的.但是实验所需时间能够减少近两个数量级.关键词：     

14N核四极共振自旋系统自旋-晶格弛豫时间的测量

¹⁴N核四极共振自旋系统的自旋-晶格弛豫是一种双指数弛豫。本文介绍了¹⁴N核四极共振自旋系统的自旋-晶格弛豫时间的3种测量方法,利用可变多面体方法对实验数据进行拟合,获得了¹⁴N核四极共振自旋系统的自旋-晶格弛豫时间T_1s和T₁₁,对有关文献中关于核四极共振弛豫时间的测量的3个观点提出了质疑。     

￣（14）N核四极共振自旋系统自旋－晶格弛豫时间的测量

￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫是一种双指数弛豫。本文介绍了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间的３种测量方法，利用可变多面体方法对实验数据进行拟合，获得了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间Ｔ＿１ｓ和Ｔ＿１１，对有关文献中关于核四极共振弛豫时间的测量的３个观点提出了质疑。     

核四极共振（NQR）

简述核能级的电四极超精细分裂及核四极共振基本原理;并就与核四极共振应用密切有关的;四极核所在处电场梯度（ＥＦＧ）张量的来源进行讨论。     

氮－14远程核四极共振谱仪

为了满足检测与探头有一定距离的含氮化合物的核四极共振信号，本文研制了一台结构简单，造价低廉的核四极共振操测仪．它利用了脉冲付里叶变换技术，可将获得的核自由感应衰减信号或者回波信号进行相干累加．整个系统分硬件和软件两大部分．前者由射频脉冲放大器（约５００Ｗ脉冲输出功率），探头，接收机，ＭＣＳ－９６型单片机和ＰＣ机构成．后者由单片机上的脉冲序列程序与ＰＣ机上的数值信号处理程序组成．利用这台谱仪，可以在几十秒时间内得到距离探头线圈１０ｃｍ内的典型￣（１４）Ｎ样品的核四极共振谱．     

14N核四极共振的偏共振效应

用虚拟１／２自旋算符讨论了核四极共振（ＮＱＲ）中自旋Ｉ＝１的自旋系统对激发脉冲宽度和频率偏置的响应。用单脉冲和双脉冲来观测的核四极共振信号与理论预期相符合。此外还证明,若只考虑射频场在分子电场梯度（ＥＰＧ）张量主轴坐标系（ＰＡＳ）中的一个轴上的分量（即有效射频场分量）的作用,就可用ＮＭＲ矢量模型来处理Ｉ＝１的核自旋系统。关键词：     

氮-14远程核四极共振谱仪

为了满足检测与探头有一定距离的含氮化合物的核四极共振信号,本文研制了一台结构简单,造价低廉的核四极共振操测仪.它利用了脉冲付里叶变换技术,可将获得的核自由感应衰减信号或者回波信号进行相干累加.整个系统分硬件和软件两大部分.前者由射频脉冲放大器(约500W脉冲输出功率),探头,接收机,MCS-96型单片机和PC机构成.后者由单片机上的脉冲序列程序与PC机上的数值信号处理程序组成.利用这台谱仪,可以在几十秒时间内得到距离探头线圈10cm内的典型¹⁴ N样品的核四极共振谱.     

相位可控的核四极矩共振激励脉冲发生器设计

在核四极矩共振（NQR）领域,射频激励脉冲信号的优劣对NQR响应信号有重要影响.针对常规方法中射频激励脉冲参数不可控的问题,本文基于32位闪存微型控制器STM32和直接数字频率合成（DDS）芯片AD9910设计了一种相位可控激励脉冲发生器.采用STM32控制AD9910产生波形参数（脉冲宽度、脉冲间隔、脉冲个数和共振频率等）可控的射频激励脉冲,利用LabVIEW软件平台设计脉冲参数设置界面,并建立计算机与微控制器通信,实现波形参数的精确优化控制.实验结果表明,该方法实现了相位可控的NQR激励脉冲序列,可为后续NQR信号检测提供有效激励源.     

旋转样品核四极共振的量子绝热微扰论分析

结合验证Berry几何相因子的Tycko旋转样品核四极共振实验,针对简并情况进一步发展并完善了作者之一最近提出的量子绝热微扰理论.应用这个理论,详细分析了任意自旋情况下具有核四极矩的旋转样品在射频场中的共振吸收,指出了可能的新的实验现象.关键词：     

Study of dynamics in pentachlorophenol in the solid state by 1D Nuclear Quadrupole Resonance exchange spectroscopy

The paper reports studies of the dynamic process in pentachlorophenol (PCP) in the solid state by one-dimensional Nuclear Quadrupole Resonance (NQR) exchange spectroscopy employing shaped rf pulses. Pentachlorophenol exhibits intramolecular hydrogen bonding between the hydroxyl proton and one of the o-chlorines. Reorientation of the hydrogen bond with migration of the hydroxyl proton from one o-chlorine to the other is possible in a wide temperature range. In this process the two o-chlorines are exchanged; at the same time this implies the exchange of the two m-chlorines as well, which we have chosen to monitor, modeling it as a two-site exchange process. A detailed analysis of the appropriate Bloch-McConnell equation is performed to formulate the relevant kinetic matrix. The exchange pulse sequence implemented by us involves suitably modulated shaped RF pulses to achieve simultaneous on-resonance excitation of the two exchanging sites. This approach results in a clear definition of the exchange time window and requires only a short experiment time. Kinetic parameters, namely, the spin-lattice relaxation rate and the exchange rate are deduced from the experimental signal intensities. Variable temperature measurements in the range 213 K–318 K have been carried out to extract the activation parameters as well.     

一种快速有效的NQR探头恢复方法

介绍了一种用于主动减小NQR探头恢复时间的Q值变换电路,它利用MOEFET控制变Q电路与探头电路的耦合,并通过变压器增加与电感线圈串联的阻抗值以达到改变Q值的目的. 此电路不会产生新的振铃也不会对接收NQR的分辨率造成损失. 实验结果表明,电路能有效缩短探头的恢复时间,同时还可以提高信噪比.     

The NQR picture of electronic phase separation in the lanthanum–barium cuprates

We report the results of Cu and La NQR investigations of the spin and charge separation in La_2−xBa_xCuO₄ compounds. For Ba doping inducing the low-temperature tetragonal phase our Cu–NQR measurements revealed three inequivalent Cu sites in CuO₂ planes. In terms of the stripe-phase picture we assign them to the charged stripe, to its neighborhood and to the AF correlated regions free of holes correspondingly. The last site corresponds to the ordered Cu magnetic moment of 0.29μ_B.     

Do Dyson Orbitals resemble canonical Hartree–Fock orbitals?

ABSTRACT

Dyson orbitals are overlaps between states with N and N±1 electrons and provide conceptual links between transition probabilities of electron detachment or attachment, density matrices, total energies and general principles of chemical bonding. Canonical, Hartree–Fock orbitals are compared with Dyson orbitals obtained with electron–propagator calculations that retain all elements of the self–energy matrix, wherein all orbital–relaxation and electron–correlation corrections to Koopmans results reside. For valence ionization energies and electron affinities of representative closed–shell molecules, canonical, Hartree–Fock orbitals usually are excellent approximations to Dyson orbitals, although there are some notable cases where the resemblance is not as strong. Numerical relationships between pole strengths and the Koopmans contributions to Dyson orbitals also are inferred from the data.     

NQR Spin Diffusion in an Inhomogeneous Internal Field

The theory of NQR spin diffusion is extended to the case of spin lattice relaxation and spin diffusion in an inhomogeneous field. Two coupled equations describing the mutual relaxation and the spin diffusion of the nuclear magnetization and dipolar energy were obtained by using the method of nonequilibrium state operator. The equations were solved for short and long times approximation corresponding to the direct and diffusion relaxation regimes.     

用时空线分析多普勒效应

采用描述波源运动，观察者运动及声波在静止空气中以声速传播的三组时空线，用几何方法导出多普勒公式，并通过时空线相交分析多普勒效应中观察者接收声波信号的时序及周期，着重讨论了一般文献中未曾涉及的不同条件下多普勒效应的结果及其物理意义。