紫外光辐照聚乙烯醇的1H NMR研究

用¹H NMR谱,自旋-晶格弛豫时间（T₁）和X-射线衍射研究了聚乙烯醇(PVA)在紫外光（UV）辐照后-OH基团与溶剂中残余水质子间氢键的生成与质子交换. 结果表明随着UV光辐照时间的增长,水峰与-OH质子峰逐渐相互靠近,同时水峰逐渐变宽,向低场方向移动,这与-OH基团与溶剂DMSO中残余水的质子之间既有氢键生成又有质子交换有关. 对辐照前后的PVA的DMSO溶液进行变温氢谱的研究,表明随着温度的升高,二者的-OH基团共振峰均逐渐变弱,溶剂残余水峰与-OH基团峰逐渐移向高场. PVA辐照前后随着浓度增大,羟基质子峰“变钝”. 辐照后的PVA的X-射线衍射表明聚集态结构中部分分子间氢键受到了破坏.     

利用核磁共振测定木材吸着水饱和含量

利用核磁共振(NMR)技术研究了室温与-3 ℃ 条件下 5 种树种木材内水分质子的自旋-自旋弛豫时间(T₂)特性,室温下各树种木材试样 T₂ 弛豫时间特性的不同是由木材微观构造导致的．通过对比冷冻前后各树种试样的信号反演峰面积,确定了其吸着水饱和含量,樟子松 38.3%,杉木 38.5%,杨木 36.0%,白蜡木 35.6%,轻木 47.6%,均高于通过吸湿外推法估算数值,与溶剂排出法、多孔板法、离心法等实测法获得的吸着水饱和含量的结果相近,核磁共振技术可作为木材内吸着水含量快速测定的实验方法．
     

丙烯腈γ辐射聚合的NMR研究

用¹H NMR、¹³C NMR谱、自旋-晶格弛豫时间（T₁）和自旋-自旋弛豫时间（T₂）研究了丙烯腈在⁶⁰Co γ射线辐射聚合后的大分子结构变化与大分子链的运动. 结果表明随着辐射剂量增大，在单体形成聚合物的过程中，聚合物主链上出现了少量的-OH基团，继续增大辐射剂量， -OH部分被氧化. 对聚合物溶液的变温氢谱的研究表明，溶剂中的残余水与上述-OH形成氢键，且随着温度升高氢键被破坏，同时H₂O与-OH之间还存在着质子交换. 利用¹³C NMR谱对丙烯腈辐射聚合的产物进行了序列结构分析. 对T₁和T₂的研究表明，辐射剂量的增大并未影响到聚丙烯腈的链运动，证明了在丙烯腈的辐射聚合过程交联反应未发生.     

固体核磁共振7Li SAE技术揭示晶体晶格中的锂离子迁移

本文采用自旋对齐回波（SAE）研究了α-LiAsF₆/PEO₆低聚环氧乙烯（PEO）分子量的体系.结果表明，自旋-晶格弛豫时间和线宽不是表征高电导率的好指标，而SAE实验的相关速率k_SAE是表征高电导率的较好指标.     

利用低温NMR技术测定木材及其热处理材纤维饱和点

实验基于核磁共振技术（Nuclear Magnetic Resonance,NMR）检测的无损性,利用低场NMR技术测定热处理前后花旗松的纤维饱和点（Fiber Saturation Point,FSP）.在-3℃和25℃条件下,对CPMG（Carr-Purcell-Meiboom-Gill）脉冲测得的信号进行横向弛豫时间（T²）分析,对比试样冷冻前后信号反演峰面积,确定试样吸着水饱和含量,得到不同热处理条件下花旗松的纤维饱和点依次为38.76%（对照材）、32.82%（180℃热处理）、29.40%（200℃热处理）、24.90%（220℃热处理）.实验结果表明,热处理温度越高,纤维饱和点越低.该结果测试结果与木材学理论相符,表明NMR技术可应用于快速确定木材纤维饱和点.     

聚酯聚氨酯分子动力学的核磁共振研究

测量了对聚酯聚氨酯在浓溶液状态下质子自旋-晶格弛豫时间随温度的变化,对其中有代表性的基团进行了详细的研究,根据BPP理论用各向同性模型计算分子局部运动的相关时间,从计算结果来看,聚酯聚氨酯的局部分子运动是符合BPP理论的,硬链段的局部分子运动比软链段的局部分子运动要慢得多,两者相差至少一个数量级以上;质子的自旋-晶格弛豫时间主要是偶极-偶极作用的影响;强烈的氢键有相互作用使得硬链段基因的局部运动相关时间接近;通过形成氢键不同的NH峰的相关时间和活化能的观察可以研究软、硬段间的相互作用。     

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。     

紫外光辐照镍系聚丁二烯的NMR研究

用¹H NMR谱,¹³C NMR谱,二维谱,X-射线衍射等方法研究了镍系高顺式聚丁二烯橡胶(NiBR) 在强紫外（UV）光辐照前后的微观结构变化和分子运动情况. 分析表明NiBR样品随着UV光辐照时间的增加,侧链乙烯基端基双键比主链端基双键更易发生氧化反应;并且随着NiBR样品的各基团的半峰宽值逐渐增加,表明NiBR在UV辐照过程中发生了部分交联反应. 样品的X-射线衍射谱图中结晶峰强度随UV光辐照时间的增加逐渐降低,表明样品的晶形无序程度增加了. 自旋-晶格弛豫时间（T₁）和自旋-自旋弛豫时间（T₂）值给出了有关NiBR辐照前后分子运动变化的信息.      

利用TD-NMR技术研究杨木高温干燥过程水分分布

木材中水分状态变化和迁移对木材的物理性质有重要影响.通过时域核磁共振技术(TD-NMR)可以从分子层面解读木材与水分的关系,可以为木材干燥、木制品加工提供理论依据和实践参考.该研究以北京杨为研究对象,通过对高温干燥过程中木材内部水分变化的自由感应衰减(FID)曲线和横向弛豫时间(T_2)进行测定与分析,探究木材干燥过程中水分状态变化及迁移过程.研究结果表明,FID和T_2信号量与木材含水率高度线性相关,由此可以计算木材在干燥过程中任意时刻的含水率.通过对干燥过程中水分T_2分布的分析表明:心材试件在干燥过程中,长弛豫时间自由水(c状态水分)的拟合面积出现了先减小后增大然后再减小的趋势,而边材试件中则不存在这种现象.在北京杨心材试件中含量最多的是弛豫时间为10 ms数量级的水分,而在边材试件中各状态水分含量差异较小,含量最多的是弛豫时间为100 ms数量级的水分.在高温干燥过程中,边材试件内各状态水分百分含量减少的速度快于心材,各试件中自由水的蒸发速度明显快于结合水.     

石墨烯低温热膨胀和声子弛豫时间随温度的变化规律

考虑到原子非简谐振动和电子-声子相互作用,用固体物理理论和方法研究了石墨烯格林艾森参量和低温热膨胀系数以及声子弛豫时间随温度的变化规律,探讨了原子非简谐振动项对它们的影响.结果表明:1)在低于室温的温度范围内,石墨烯的热膨胀系数为负值,随着温度的升高,其热膨胀系数的绝对值单调增加,室温热膨胀系数为-3.64×10~(-6)K~(-1);2)简谐近似下的格林艾森参量为零.考虑到非简谐项后,格林艾森参量在1.40-1.42之间并随温度升高而缓慢增大,几乎成线性关系,第二非简谐项对格林艾森参量的影响小于第一非简谐项;3)石墨烯声子弛豫时间随着温度的升高而减小,其中,温度很低(T10 K)时变化很快,此后变化很慢,当温度不太低(T300 K)时,声子弛豫时间与温度几乎成反比关系.     

小白鼠肌肉组织的NMR质子自旋交换分析

本文在Zimmerman-Brittin两相质子交换核磁共振弛豫模型基础上,分析了NMR弛豫实验中检测信号与各相表现和本征弛豫多数的关系,编写了自动化处理实验数据的计算机程序,这一技术可用于复相系统中不同成分的NMR表现和本征弛豫特性研究中,本文中的样品是选用健康新鲜的小白鼠肌肉,没加任何处理,用h-h,s-h,s-s脉冲序列,反转恢复法(π-τ-π/2)在强场下(0.92T)做T₁、T₂测定实验,分析结果表明本征弛豫参数T₁=1050ms,T₂=4500μs的成分是由肌肉中的"自由水"引起的,其质子相对含量为69%;本征弛豫参数T₁=530ms,T₂=26μs的成分是由肌肉中的"束附水"引起的,其质子相对含量为9%,本征弛豫多数T₁=530ms,T₂=1250μs的成分是由肌肉中的各种大分子和有机物引起的,其质子相对含量为9%,本征弛豫参数T₁=470ms,T₂=1250μs的成分由样品中的脂肪引起的,其质子相对含量为13%,在肌肉组织中的质子与水中质子之间有强烈的交换作用,其交换率k=1000s^-1.在脂肪中的质子与其它成分之间没有交换作用。     

On- and off-resonance spin-lock MR imaging of normal human brain at 0.1 T: possibilities to modify image contrast

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T_1ρ) and off-resonance spin lock relaxation parameters (T_1ρ^off, M_e/M_o), MT parameters (T_1sat, M_s/M_o), and T₁, T₂ were determined for the cortical gray matter, and for the frontal and parietal white matters. The T_1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T_1ρ^off for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B_eff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T_1ρ of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T_1ρ^off decreased significantly with increasing θ (p < 0.001). T_1ρ and T_1ρ^off with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.     

Quantitative NumART2* mapping in functional MRI studies at 1.5 T

Quantitative mapping of the effective transverse relaxation time, T₂* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART₂* (Numerical Algorithm for Real time T₂*). Comparisons between NumART₂* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T₂* value, relative changes in T₂* remained unaffected. Statistical analysis of the T₂* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART₂* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART₂* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T₂* maps.     

测量电子自旋——晶格弛豫时间T1的技术问题

本文讨论应用连续波方法测量电子自旋——晶格弛豫时间T₁的实验技术问题。分析液氮翻滚使T₁测量结果很不一致的原因,提出用吹冷气冷冻样品方法,可以解决液氮翻滚对测量T₁所产生的影响.用改进的方法测量ZnS:Mn、Cu粉末样品的T₁,获得重复性较好的实验结果。     

T2 relaxation time histograms in multiple sclerosis

An accurate measurement of the transverse relaxation time T₂, and the histogram of T₂ in the brain parenchyma can be accomplished in vivo using a multi-echo magnetic resonance imaging sequence. An estimate of the error in the T₂ measurement is derived using copper sulfate doped water phantoms. Correction factors are calculated and applied to the signal intensity of each voxel prior to the in vivo T₂ evaluation. These corrected T₂ are in good agreement with the theoretical values calculated from copper sulfate concentrations. This technique is then applied to calculate T₂ histograms of the brain. The population studied was composed of normal volunteers and multiple sclerosis patients. The corrected T₂ histogram method discriminates the normal control population from the MS population, and also discriminates between relapsing-remitting patients and primary progressive or secondary progressive patients. Moreover using this approach we are able to detect in MS patients a global shift of the T₂ of the white mater toward higher values. The results of this study showed that the method is easy to implement and may be used to characterize MS pathology.     

Multicomponent water proton transverse relaxation and T2-discriminated water diffusion in myelinated and nonmyelinated nerve

The influence of compartmental boundaries on water proton transverse relaxation and diffusion measurements was investigated in three distinct excised nerves, namely, the non-myelinated olfactory nerve, the Schwann cell myelinated trigeminal nerve, and the oligodendrocyte myelinated optic nerve of the garfish. The transverse relaxation decay curves were multiexponential and their decomposition yielded three primary components with T₂ values 30–50, 150, and 500 ms, which were subsequently assigned to water protons in the myelin, axoplasm, and interaxonal compartments. The short T₂ component was absent in the non-myelinated olfactory nerve, but present in both myelinated nerves and thus provides supporting evidence for the use of quantitative T₂ measurements to measure the degree of myelination. The signal contribution of each T₂ component to the apparent diffusion coefficient measurements was varied by incrementing the spin-echo time with a preparatory CPMG train of radiofrequency pulses. The apparent diffusion coefficient and its anisotropy were shown to be independent of the spin-echo time over the range of 70 to 450 ms.     

钙钛矿薄膜气相制备的晶粒尺寸优化及高效光伏转换

钙钛矿薄膜的气相制备是一种极具潜力的工业化生产工艺,但薄膜的质量控制目前远落后于溶液制备法.本文通过建立PbI_2薄膜向钙钛矿薄膜完全转化过程中反应时间、晶粒尺寸与温度的关系,实现了薄膜的质量优化及大面积钙钛矿薄膜的制备,将薄膜的平均晶粒粒径从0.42μm优化到0.81μm.基于空间电荷限制电流模型对缺陷密度的研究显示,钙钛矿薄膜的缺陷密度由5.90×10~(16)cm~(–3)降低到2.66×10~(16)cm~(–3).光伏器件(FTO/TiO_2/C_(60)/MAPbI_3/spiro-OMeTAD/Au结构)测试显示,面积为0.045cm~2器件的平均光电转换效率从14.00%提升到17.42%,最佳光电转换效率达到17.80%,迟滞因子减小至4.04%.同时,基于180℃制备的1cm~2器件的光电转换效率达到13.17%.     

环氧树脂高温分子链松弛与玻璃化转变特性

环氧树脂是电力设备中广泛应用的一种绝缘材料, 其介电性能受到分子链运动特性的影响. 本文制备了直径为50 mm、厚度为1 mm的环氧树脂试样, 采用差示扫描量热仪和宽频介电谱仪测试了环氧树脂的玻璃化转变温度和介电特性. 实验结果表明, 环氧树脂的玻璃化转变温度为105 ℃, 在玻璃化转变温度以上, 高频段出现了由分子链段运动造成的松弛过程, 低频段出现了由载流子在材料中迁移造成的直流电导过程. 发现环氧树脂不同尺寸分子链段的松弛时间不同, 其松弛时间分布较宽, 计算得到了分子链段在不同温度下的松弛时间分布特性. 分子链松弛峰频率和直流电导随温度的变化关系服从Vogel-Tammann-Fulcher公式. 拟合实验结果得到分子链松弛峰频率和直流电导的Vogel温度和强度系数. 由Vogel温度计算得到了与差示扫描量热测试结果一致的玻璃化转变温度, 约为102 ℃. 结果表明玻璃化转变温度以上环氧树脂的自由体积增大, 分子链段有足够的空间来响应外电场从而产生分子链松弛极化, 载流子有足够的能量在材料中迁移形成电导.     

High field magnetoresistance of CeAl2 at low temperatures

We have measured the magnetoresistance ρ(H,T₀) of the magnetic Kondo lattice CeAl₂ at temperatures T₀ in the range 0.035 – 1.3 K, well below the Néel temperature T_N=3.8 K, in magnetic fields H up to 145 k0e. The ρ vs H curve exhibits a rapid decrease between H=45–65 kOe corresponding to the metamagnetic transition at H=H_M. The resistivity then levels out to a value which depends only weakly on field and temperature. For HM a small positive magnetoresistance was observed with the derivative dρ/dH increasing as the temperature is lowered. The present results are compared with the ρ(H,T₀) data obtained for the CePb₃ magnetic Kondo lattice, where the decrease in the resistivity at HH_M was considered earlier to be evidence of field induced superconductivity.     

Mn掺杂Zn-In-S量子点的制备及发光性质研究

制备了Mn掺杂Zn-In-S量子点并研究了Zn/In的量比和反应温度对其发光性质的影响。在Mn掺杂的Zn-In-S量子点的发光谱中观测到一个600 nm发光带。通过改变Zn/In的量比,掺杂量子点的吸收带隙可从3.76 e V(330 nm)调谐到2.82 e V(440 nm),但600 nm发光峰的波长只有略微移动。这些掺杂量子点的最长荧光寿命为2.14 ms。当反应温度从200℃增加到230℃时,掺杂量子点的发光强度增加并达到最大值;而继续升高温度至260℃时,发光强度迅速减弱。此外,测量了Mn掺杂Zn-In-S量子点的变温发光光谱。发现随着温度的升高,发光峰位发生蓝移,发光强度明显下降。分析认为,Mn掺杂Zn-In-S量子点的600 nm发光来自于Mn2+离子的4T1和6A1之间的辐射复合。