共振介质中极化强度的经典振子描述

文章用经典振子模型,讨论共振跃迁介质中宏观极化强度的驰豫过程;用图形说明了单个振子由于辐射而产生的驰豫过程和振子间由于弹性碰撞而产生的驰豫过程;介绍了影响驰豫时间的因素和几种典型介质的驰豫时间;由振子模型推导了共振介质的线性极化率公式.     

1H驰豫时间谱在水泥基材料研究中的应用

水泥水化、硬化体结构的形成及演化、水泥基材料内部不同水分之间的转化、吸水、干燥、水分在水泥基材料内部的扩散过程引起水分化学状态或所处环境物理状态的变化.这种变化可用1H核磁共振驰豫时间进行表征.已有的研究表明,1H驰豫时间谱可用于水泥水化过程、硬化体结构形成、孔结构、水分在水泥基材料内的传输过程等的表征,所得结果与其它方法所得结果有较好的一致性.且磁共振成像可直接观察水分在水泥基材料中的分布及传输,这是其它现代测试方法难以达到的.     

核磁共振技术研究环糊精包合物的相互作用

综述了用核磁共振技术研究环糊精包合物的方法,包括1H NMR、13C NMR、2D NMR以及扩散实验和测量驰豫时间等技术在环糊精与客体相互作用信息以及在环糊精包合物结构解析方面的应用。     

低场核磁共振技术在槟榔水分测定中的应用

为了准确和高效评估槟榔的新鲜程度，利用低场核磁共振技术对干燥过程中的槟榔进行成像及驰豫时间(T₂)采集，研究槟榔干燥过程中水分迁移及水分状态变化规律，建立一种快速无损检测槟榔含水率的方法。结果表明，槟榔鲜果中共存在三种水分状态：自由水、不易流动水和结合水，而自由水占比90%以上。在干燥过程中，自由水含量快速降低，结合水含量占比逐渐上升，槟榔水分含量与驰豫时间(T₂)反演谱图总峰面积呈显著正相关，拟合方程为y=164.9x+62.686(R²=0.9969);槟榔水分含量与衰减曲线首峰点值呈显著正相关，拟合方程为y=165.58x+19.892(R²=0.9979)。经过验证模型，槟榔含水率在20%以上时，真值与拟合值相对误差控制在5%以内，可用低场核磁共振技术对槟榔含水率进行快速无损检测。     

基于朗道-利夫席茨-吉尔伯特方程的自旋阀动力学研究进展

巨磁阻效应的发现开辟了自旋电子学研究的新时代.目前,自旋电子学已经发展成为与磁学、半导体、微电子学、凝聚态物理等学科紧密结合的新学科.在自旋电子学研究中自旋阀结构,包括垂直自旋阀和横向自旋阀,发挥了至关重要的作用并成为各类自旋电子器件设计的基础.借助于各种自旋阀器件,人们又相继发现了Slonzeweski自旋转移矩、类场矩、自旋霍尔效应、自旋轨道矩等重要物理效应.本文将综述这些物理效应的概念及应用前景、面向应用需要解决的问题等等.我们将重点关注基于朗道-利夫席茨-吉尔伯特方程的动力学研究的进展情况.     

新型非局域磁纳米开关的原理和研究进展

利用磁体进行信息记录的器件都需要操控磁体的磁矩,即使得磁体的磁矩翻转(磁化反转),从而实现"0"和"1"的信息转化。目前,实现纳米磁体磁矩翻转的方法主要有3种,即最传统的利用外磁场的方法、利用自旋转矩方法和利用自旋轨道矩的方法。后2种基于自旋矩的磁矩操控方法不需要外磁场,方便而且节能,不论是技术层面还是物理层面,都为科技人员展开了辽阔的研究空间。自旋轨道矩的发现始于近年自旋轨道耦合的研究,特别是自旋霍尔效应的研究。自旋霍尔效应和逆自旋霍尔效应现在被公认为是一种自旋操控的有效手段,它通过对铁磁/非磁双层系统上的铁磁体施加自旋矩使其磁矩翻转,并能探测由自旋注入或泵浦方法产生的自旋电流。本文综述了基于自旋霍尔效应等新物理效应的纳米磁体磁矩翻转的原理和研究进展情况。从应用和测量观点出发,磁矩翻转的非局域控制对于发展新型磁存储等自旋电子器件具有更大意义。本文介绍了几种主要的非局域自旋器件对材料的要求,对几种主要的材料参数进行了初步汇总。     

非共线横向自旋阀结构逆自旋霍尔效应

逆自旋霍尔效应是测量材料自旋输运参数(比如自旋霍尔角、自旋扩散长度等)的重要手段。目前关于逆自旋霍尔效应的实验研究比较多,但理论计算相对缺乏。发展高效精准的计算方法十分重要。本文计算了横向自旋阀结构中,逆自旋霍尔信号随磁铁非共线角度的变化关系。我们的计算针对目前最具前景的常规合金Cu Bi和Cu Ir展开。结果表明Cu Bi的逆自旋霍尔信号最强。对计算的一些困难(比如接触电阻的确定等)也做了讨论。结果对深入理解自旋输运具有一定价值。     

基础理论

20063021用1H-双量子过滤NMR自旋-扩散实验研究熔纺尼龙6纤维的复合形态Buda A.…;Chem.Phys.Chem.,2004,5(6),p.876(英)用1H-双量子过滤NMR自旋-扩散实验研究用D2O2水化的高速熔纺尼龙6纤维的复合形态。采用自旋-扩散三维方程式模拟沿着原纤和原纤间选定的结晶区的磁场变化。自旋-扩散三维方程式近似于一维分析NMR信息,一维分析NMR信息相应于片晶形态。由此可以测得晶体尺寸,少流动的无定形区大小以及原纤的直径和原纤间的距离。研究了一系列极端卷绕速度和拉伸时的尼龙6纤维。用广角X-射线衍射和小角X-射线衍射得到的数据表明沿…     

弛豫型铁电单晶Pb(Mg1/3Nb2/3)O3 - PbTiO3电畴结构与铁电性能的关系

驰豫型电单晶Pb(Mg1/3Nb2/3)O3-PbTiO3[PMNT]的电畴结构与铁电性能随组分变化：由纯PMN至PMNT67／33晶体,晶体铁电性能由驰豫型铁电体向正常铁电体方向转变,电畴结构同微畴－不规则宏畴－规则宏畴演化,压电性能逐步增强。电畴类型的转化也可由电场和温度诱导。三方相PMNT晶体（001）与（111）切型晶片在极化后仍维持多畴态,它们在压电性能上的差异可从畴壁运动与两相共存方面获得解释,尽管受晶体组分与结构起伏的影响,电畴分布的不均匀性在退火与极化前后始终存在,但晶体生长后期的退火处理与极化条件的改善对调节电畴结构、提高压电性能仍有一定效应。     

氧化物玻璃中Eu~(3＋)离子的发光研究

应用荧光光谱、红外振动光谱和差热分析等研究了Ｅｕ３＋离子在不同氧化物玻璃基质中的发光行为。结果表明：不同氧化物玻璃基质对Ｅｕ３＋离子的激发谱和发光谱的峰位影响很小，发光强度按硅酸盐、硼酸盐、钡磷酸盐、铝磷酸盐玻璃顺序递增。玻璃中Ｅｕ３＋激活离子与最邻近配位体之间共价键因素引起的近距离作用对无辐射跃迁过程影响比多声子驰豫更强烈，讨论了氧化物玻璃配位体对Ｅｕ３＋离子的极化作用与发光强度的关系。     

缓凝剂SN-3的制备及其对水泥浆横向弛豫时间T2分布的影响

首先合成了一种新型两性聚合物缓凝剂SN-3,然后采用红外光谱和元素分析等测试手段对其进行结构表征。其次,对其应用性能作了进一步研究,主要包括稠化时间、加量和温度敏感性等,实验结果表明应用性能满足现场施工要求。利用低场核磁共振测试技术重点研究了缓凝剂SN-3对油井水泥浆水化过程中横向弛豫时间T₂分布的影响,在相同的水灰比、温度和水化时间下,对纯水泥浆C和掺有缓凝剂SN-3的水泥浆CHN的横向弛豫时间进行测试和分析,借助迁移速率和峰形指数两个参数表征水泥浆T₂分布曲线的变化过程。最后,结合X衍射和扫描电镜（SEM）进一步探讨缓凝剂SN-3的缓凝作用原理。实验结果表明,缓凝剂使水泥浆中填充于絮凝结构之间的水的受缚程度减小,存在时间变长,转化为化学结合水所经历时间变长;缓凝剂SN-3主要通过沉淀和络合作用达到缓凝效果的。     

The novel antimalarial compound dioncophylline C forms a complex with heme in solution

A structural model of the complex formed between the novel antimalarial compound dioncophylline C (DioC) and its presumed target ferriprotoporphyrin IX heme (FPIX) is presented. The complex structure was calculated with molecular dynamics (MD) simulations using intermolecular distance restraints between DioC and the iron center in FPIX, determined from NMR paramagnetic relaxation. Besides the spin state of the iron and longitudinal relaxation rates of hydrogen nuclei in DioC, the effective correlation time of paramagnetic relaxation was determined from NMR measurements at three different magnetic field strengths. The derived structural model shows high similarity to complexes formed by FPIX and antimalarials of the quinoline family (chloroquine, quinine, quinidine, and amodiaquine). The conformation of DioC is sterically stabilized by a water molecule coordinated to iron in FPIX. This structural feature may provide an important hint at possibilities for a further optimization of novel naphthylisoquinoline alkaloid (NIQ) antimalarial drugs.     

The Molecular Origin of Nuclear Magnetic Relaxation in Methyl Cellulose and Hydroxypropylmethyl Cellulose

Nuclear magnetic relaxation processes in methyl cellulose (MC) and hydroxypropylmethyl cellulose (HPMC) were studied by proton spin-lattice NMR relaxation. The proton relaxations were measured in the temperature range 90–420 K at 90 MHz. At low temperature the proton spin-lattice relaxation is caused by the modulation of the methyl proton-proton dipole-dipole interactions by the reorientation of the methyl groups. In this temperature range the spin relaxation vs. temperature data were interpreted with the model of dynamical inequivalence of methyl groups: two in MC and three in HPMC. The dynamical parameters were calculated for each of these groups. The segmental motion of the MC and HPMC chain via the glucosidic bond which corresponds to the local chain motion of these polymers is the dominant mechanism of the proton spin-lattice relaxation time above 250 K.     

Solid state and proton relaxation NMR study of Dipteryx alata Vogel

The knowledge of polysaccharides obtained from fruit seed and its chemical characteristics are important to evaluate their final properties, as well as their uses and benefits. Solid state nuclear magnetic resonance (NMR) has been used to evaluate the behavior of the samples, since NMR permits to evaluate both chemical and dynamic molecular behavior of polysaccharides, because they are amorphous and heterogeneous. The NMR analyzes were carried out using high and low field NMR techniques. The results obtained from high field showed the main chemical constituents present in the seeds and seed flour. Through low field NMR different domains with their own molecular mobility and interactions were observed; due to the measurements of proton spin‐lattice relaxation time (T₁H). According to the results obtained for Cumbaru seed, solid state NMR showed to be a powerful source to characterize fruit seed flour. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

基于低场核磁共振的煤粉动态吸附测量

煤层气的开发是我国非常规天然气开发的重要环节，与常规天然气不同的是煤层气中甲烷主要以吸附形式赋存在煤的一系列纳米孔中。甲烷在煤粉颗粒孔隙中吸附行为的动态过程对煤层气的开发具有重要意义。实现了一种基于低场核磁共振技术在线测量煤粉吸附特性的实验方法，通过横向驰豫分布区别孔隙中含氢流体分布，定量表征游离气和吸附气含量。结果表明煤粉颗粒的甲烷吸附在核磁共振的横向弛豫图谱中呈现多峰分布，其中弛豫时间在0.1～1 ms的峰包含了纳米孔隙中甲烷含气量的信息。随着时间增加，甲烷气体逐渐转换为吸附态。通过不同压力下核磁共振的横向弛豫图谱，定量分析了甲烷在颗粒样品中随时间和压力变化的动态吸附过程，并得到了等温吸附曲线且符合Langmuir拟合模型。     

NMR characterization of absorbed water in equilibrium swollen hydrogel P(AM‐NaA)

The behavior of absorbed water in equilibrium‐swollen poly(acrylamide‐co‐sodium acrylate) [P(Am‐NaA)] hydrogel is studied with ¹H nuclear magnetic resonance (¹H‐NMR). The observed non‐exponential decay of the spin–spin relaxation data manifests at least two distinguishable environmental states of the absorbed water in all samples. The component, characterized by the relatively shorter T₂, is associated with the more tightly bound water; whereas the other, characterized by longer T₂, might be a combination of near normal and loosely bound water. Attention is directed to the way in which relaxation times and the corresponding fraction of each type of water behave as a function of the crosslink density at 25°C. There is evidence of a sudden change of the crosslink state in P(Am‐NaA) hydrogel at crosslink density of about 1.0%. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1203–1207, 1999     

缓凝剂对水泥浆中自由水状态演变的影响

用低场核磁共振技术考察了HN-1型缓凝剂对水泥浆体中可蒸发水的横向弛豫时间(T2)及状态演变过程的影响。结果表明:在初始水化阶段的150 min内,水泥浆GR(添加缓凝剂HN-1的水泥净浆)的弛豫峰峰形和峰顶位置均无明显变化,水泥浆G(纯水泥净浆)的弛豫峰峰形变窄且峰顶位置从2.15 ms迁移至0.95 ms,说明缓凝剂HN-1主要通过改变水泥浆体中不同状态水的存留时间来改变其水化进程。随养护时间的延长,硬化水泥石W0.44和WR0.5中可挥发水弛豫峰分布范围分别从0.11~4.75 ms变为0.08~0.58 ms、0.24~4.23 ms变为0.11~2.35 ms,总体趋向于短弛豫时间,表明水泥石中毛细水逐渐向凝胶水和物理结合水转化,水泥石养护龄期延长至25 d时,其内部凝胶结构水含量超过90%。利用XRD考察了缓凝剂对水泥浆水化产物的影响,结果表明:缓凝剂只改变水泥浆水化过程,对最终水化产物晶型及晶型结构不存在任何影响。     

1H-NMR imaging study of molecular mobility in carbon black-filled,TBBS–sulfur-vulcanized cis-polyisoprene

The distributions of the T₂ relaxation times in carbon black filled, TBBS-Sulfur vulcanized cis-polyisoprene were were studied using ¹H NMRI spin–echo experiments. It has been reported that more than two T₂ relaxation times are observed in carbon black-filled rubbers, reflecting the existence of the hard regions adjacent to the crosslinks or filler particle and soft regions distant from such rigid components. Our current concern is how the amount and distribution of the T₂ times are affected by the filler incorporation in the rubber compounds. A decrease in the T₂ relaxation times with an increasae in carbon black content is observed. The average T₂ time, 〈T₂〉, drops from 11.38 ms with no carbon black to 10.05 ms with 15 phr carbon black. The 〈T₂〉 further decreases when the black loading level is increased form 15 to 30 phr and 30 to 50 phr, but the magnitude of the changes in the 〈T₂〉s are not as large as in the initial loading (0 to 15 phr). The observations of the 〈T₂〉s suggest inhomogeneities are induced in the network structure by the black incorporation. The distribution of the T₂ relaxation times becomes narrower as the black loading level increases. There are at least four factors governing the intensity of the images in the swollen, filled rubber vulcanizates as well as the NMR parameters (T₁, T₂, T_R, and T_E: (1) ¹H spin density, (2) inhomogeneity of the network structure, (3) degree of swelling in the sampling solvent, and (4) displacement effect of the carbon black. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1385–1390, 1998     

Characterization of crosslinked starch materials with spectroscopic techniques

The structure, mobility, and properties of crosslinked starch materials of various compositions were investigated with FTIR and NMR spectroscopy, and relaxation time measurements were taken with cross‐polarization/magic‐angle‐spinning (CP–MAS) and magic‐angle‐spinning (MAS) spectroscopy. Characterization by Fourier transform infrared spectroscopy confirmed the crosslinking reaction. The CP–MAS and MAS spectra allowed the assignment of the principal ¹³C signals. The molecular mobility of these polysaccharides was analyzed in terms of the cross‐relaxation time between the protons and carbons, the ¹H spin–lattice relaxation time in the rotating frame, and the ¹H longitudinal spin–lattice relaxation time. Relaxation studies showed that increasing the crosslinking degree increased the amorphous content, and the material became rigid as an increasing number of covalent bonds in the polymer network reduced mobility. The values of the spin–lattice relaxation in the rotating frame reflected the homogeneous nature of the materials. The correlation between the crosslinking degree, structure, and mobility and the sorption properties of these sorbents was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2650–2663, 2004