不同荷载水平及速率下超软土水相核磁共振试验研究

大规模建设中面临越来越多的淤泥等超软土地基处理,其目的是尽可能排出超软土体中的水而使土体固结,以改善其物理力学性能.静动力排水固结法试图利用高能量冲击而将超软土中部分结合水转换为自由水,进而实现更多水的排出而有效固结.然而,目前还不十分清楚能造成这种水相变化的冲击荷载究竟要达到何种水平及速率.为此,在模拟条件的、淤泥土的不同类型荷载水平及速率试验基础上,进行核磁共振水相测试,探索了典型荷载水平及速率下这种超软土中结合水可转化为自由水的条件及规律,主要为:1)对应于通常工程荷载的较低能量真三轴试验荷载速率与水平(1.6 MPa/s与100 kPa及以下),淤泥类超软土中非自由水不能转化为自由水.2)对应于静动力排水固结法条件的高速冲击荷载下(每击荷载水平3787 kPa,速率631.2 MPa/s),非自由水可转化为自由水;且冲击总能量越大(遍数及击数越多),就越易析出自由水.3)约束样品的侧限刚度对非自由水转化为自由水的影响可忽略.     

核磁共振T2谱换算孔隙半径分布方法研究

岩芯核磁共振T2谱和压汞分析数据均在一定程度上反映了岩石的孔隙结构特征,理论分析和二者频率分布图对比表明,这两组数据有较好的相关性,核磁共振T₂谱能够换算为反映岩石孔隙结构特征的孔隙半径分布图. 本文应用最大相关性原理、最小二乘法及插值算法等数学方法,给出了一个改进的将T2谱换算为孔隙半径分布图的实用有效新方法,求得了T2弛豫时间与岩芯孔隙半径r之间的换算系数C,计算过程中着重对比了T₂谱与压汞数据的主要分布区间,并考虑了压汞进汞饱和度小于100%对换算结果的影响. 天然砂岩岩芯核磁共振T₂谱换算为孔隙半径分布图的实际应用效果表明,着重对比T₂谱与压汞数据的主要分布区间,同时考虑压汞进汞饱和度小于100%对换算结果的影响是必要的,换算结果更加真实可信.     

岩心核磁共振实验对低孔低渗碳酸盐岩储层的适应性研究

低孔低渗碳酸盐岩储层矿物成分复杂、岩石骨架参数难以确定、储集空间类型多样、孔隙结构及孔渗关系复杂、常规测井曲线响应特征不明显,使其测井评价极其困难．本文利用核磁共振测井定量评价低孔低渗碳酸盐岩储层岩心的孔隙结构、计算储层参数．利用T₂谱分布曲线分析孔隙结构、计算T₂截止值;在此基础上计算岩心总孔隙度、有效孔隙度、束缚水孔隙度、渗透率等储层参数,并与常规岩心实验结果进行对比分析;最后,总结出核磁共振测井在低孔低渗储层中的应用优势与局限,为核磁共振测井评价模型的建立提供基础数据．     

相同条件下定频、变频空调节能舒适性对比试验研究

在焓差实验室中模拟家用空调器的实际运行环境,相同条件下对比研究相同制冷量的定频和变频空调器的节能舒适特性。结果表明:相同条件下定频空调器能使室内更早的达到设定温度,当空调器设定温度16℃,室外温度35℃时,定频和变频空调器的耗电量达到相同的时间为11h,室外温度为40℃时,定频和变频空调器的耗电量达到相同的时间为6.3h,室外温度越高,定频和变频空调器耗电量相同的时间越提前,变频空调器需要更长的时间才能体现出节能优势;室外温度35℃时,运行变频和定频空调器,室内不同高度之间的温差分别在0.2℃~0.5℃和0.7℃~1℃,室内温度波动周期分别为2.4h和0.25h,变频空调器温差低于定频空调器,且波动周期大,室内温度变化缓慢,舒适性优于定频空调器。     

冲击荷载下颗粒物质缓冲性能的试验研究

颗粒物质是一种复杂的能量耗散体系. 颗粒间的摩擦和黏滞作用可使冲击荷载引起的能量有效衰减, 颗粒间的力链结构又可将瞬时局部冲击荷载进行空间扩展和时间延长, 达到良好的缓冲效果. 为研究颗粒物质对冲击荷载的缓冲性能, 本文采用重力作用下球体冲击筒内颗粒物质的试验系统, 研究了筒体底部作用力在颗粒材料、颗粒厚度等因素影响下的变化规律. 试验结果表明: 非规则颗粒具有更加良好的缓冲性能, 粗颗粒的缓冲性能略高于细颗粒. 颗粒厚度H是影响缓冲性能的重要因素, 并存在一个临界厚度H_c. 当H<H_c时, 缓冲性能随H的增加而增强; 当H>H_c时, H对缓冲效果的影响不再显著. 以上研究是在同一冲击能量下进行的, 而对于不同冲击能量下的H_c还需要深入开展. 通过颗粒物质对冲击荷载缓冲性能的试验研究, 可揭示颗粒材料的基本物理力学行为, 为其在缓冲减振领域中的应用提供依据.     

早龄期荷载及低温作用下的混凝土声发射特征试验研究*

井壁混凝土由于施工与环境特殊性导致其裂缝扩展情况异常,本文通过对不同早龄期荷载、低温条件下混凝土轴压破坏过程的声发射检测,分析井壁施工环境对混凝土内部裂缝产生、发展的影响。研究表明,早龄期荷载、低温单独作用时,与标养混凝土主要差异在轴压过程中的声发射初始阶段,对混凝土内部的原有收缩裂缝有所影响。当两者耦合作用时,早龄期荷载影响比低温作用显著,并且在早龄期荷载较大时会出现声发射信号"倒置"现象。     

固体核磁共振结合密度泛函理论计算研究SSZ-39分子筛的钠离子落位与铝分布

具有AEI结构的SSZ-39分子筛的骨架外阳离子落位和铝分布对其催化性能影响显著.AEI笼中有三个结晶学不等价位,且铝取代T位具有一定的倾向性.本文结合固体核磁共振（NMR）技术（²⁷Al/²³Na MQ MAS NMR）,以及密度泛函理论（DFT）计算,研究了不同硅铝比Na-SSZ-39分子筛中的Na⁺落位和铝分布.在孤立铝分布的情况下,铝原子优先占据于T3位,Na⁺主要落位于AEI笼中的SIIa0和SIII'a0位点上,其中SIII'a0位点的优先度较高,此外少部分Na⁺还落位于六棱柱内部的SIa0.当铝对存在时,AlSiSiAl分布的铝对占据六元环的对位（T3-T3）,对应的Na⁺分别落位于SIIa1和SⅢ'a1位点.随着分子筛结构的部分破坏,游离的Na⁺可能形成明显的SIII'b位点.本文可加深对SSZ-39分子筛构效关系的理解,为更好地调控催化性能奠定基础.     

三点弯曲试验 条件下花岗岩声发射横纵波特征及损伤演化*

开展花岗岩三点弯曲试验,利用横纵波两种传感器接收花岗岩破坏过程的声发射信号,对比分析声发射横纵波信号的时频特征,在此基础上,基于声发射横纵波建立损伤变量,探讨花岗岩三点弯曲条件下损伤演化规律。研究结果表明：花岗岩破坏过程声发射横纵波事件率变化趋势较为相似,临近峰值载荷时均加速上升,破坏时达到峰值,但纵波事件率加速点早于横波事件率;声发射横纵波能率变化趋势一致,呈现峰前低水平稳定变化、峰后陡升到峰值的特征。声发射横纵波主频在临近峰值载荷逐渐形成主频条带,但其频率存在差异,纵波主频分布在0~10 kHz、30~50 kHz和100~110 kHz,而横波主频集中分布在0~10 kHz。相比纵波损伤变量,横波损伤变量能够刻画峰后损伤急速发展的过程,能较好地表征花岗岩三点弯曲作用下损伤变化规律。     

超临界高压动叶栅壁面静压分布的试验研究

在低速风洞上对某型超临界汽轮机高压级动叶栅进行了静态试验.详细测量总压损失由栅前至栅后的发生与发展以及静压系数在不同叶高沿叶型的分布.试验结果表明,具有后部加载叶型的正弯动叶片栅气动特性优良,叶型损失与二次流损失较小,出口气动参数沿叶高分布均匀,并且具有良好的冲角适应性.     

Nuclear magnetic resonance diagnosis of an anaplastic astrocytoma

A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T₂ (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients.     

核磁共振技术在生物研究中的应用

核磁共振（nuclear magnetic resonance,NMR）是以原子核自旋的共振跃迁为探测对象的谱学方法.当自旋量子数不为零的原子核处于外磁场中时,会引起能级的Zeeman分裂.若再施加能量等于Zeeman能级差的射频场,则会诱发原子核自旋的共振跃迁,这种现象即为核磁共振.核自旋的共振频率与原子的类型有关,且受原子所处化学和物理环境的影响.此外,NMR能量较低,不会影响探测对象（常为分子）的状态.因此,NMR能够在无损条件下提供多种具有原子和分子分辨的物质组成、结构、形态、动态变化等丰富信息.     

核磁共振技术在生物研究中的应用

核磁共振(nuclear magnetic resonance,NMR)是以原子核自旋的共振跃迁为探测对象的谱学方法.当自旋量子数不为零的原子核处于外磁场中时,会引起能级的Zeeman分裂.若再施加能量等于Zeeman能级差的射频场,则会诱发原子核自旋的共振跃迁,这种现象即为核磁共振.核自旋的共振频率与原子的类型有关,且受原子所处化学和物理环境的影响.此外,NMR能量较低,不会影响探测对象(常为分子)的状态.因此,NMR能够在无损条件下提供多种具有原子和分子分辨的物质组成、结构、形态、动态变化等丰富信息.     

Nuclear magnetic resonance studies of vortices in high temperature superconductors

The distinct distribution of local magnetic fields due to superconducting vortices can be detected with nuclear magnetic resonance (NMR) and used to investigate vortices and related physical properties of extreme type II superconductivity. This review summarizes work on high temperature superconductors (HTS) including cuprates and pnictide materials. Recent experimental results are presented which reveal the nature of vortex matter and novel electronic states. For example, the NMR spectrum has been found to provide a sharp indication of the vortex melting transition. In the vortex solid a frequency dependent spin–lattice relaxation has been reported in cuprates, including YBa₂Cu₃O_7-x, Bi₂SrCa₂Cu₂O_8+δ, and Tl₂Ba₂CuO_6+δ. These results have initiated a new spectroscopy via Doppler shifted nodal quasiparticles for the investigation of vortices. At very high magnetic fields this approach is a promising method for the study of vortex core excitations. These measurements have been used to quantify an induced spin density wave near the vortex cores in Bi₂SrCa₂Cu₂O_8+δ. Although the cuprates have a different superconducting order parameter than the iron arsenide superconductors there are, nonetheless, some striking similarities between them regarding vortex dynamics and frequency dependent relaxation.     

扫场对核磁共振测量的影响

在连续波核磁共振实验中，通常采用低频扫场产生重复再现的共振吸收信号。当处于磁场中的射频线圈引线回路等效面积不为零时，简谐扫场必然引起该闭合回路的磁通量变化，由此而产生同频简谐感生电动势并与核磁共振信号叠加共同构成振荡器输出信号。由于扫场上升和下降过程的感生电动势方向相反，从而扫场前半周和后半周所对应的共振吸收测量信号存在差异。实验结果表明：扫场强度及方向对核磁共振测量影响来源于实验测量技术缺陷，而非核磁共振的物理本质。     

Nuclear magnetic resonance study of iron overload in liver tissue

Whole-tissue and homogenized samples of human liver were studied in a NMR spectrometer, T1 and T2 relaxation times were measured as a function of added inorganic or organic iron. When inorganic iron (Fe+3) was added, pronounced T1 and T2 shortening was noted. However, when organic iron, in the form of ferritin, was added, the amount of T1 and T2 relaxation enhancement was much reduced for the same amount of added iron. The in vitro ferritin results model the situation found in clinical studies of hemochromatosis. Only in cases of severe iron overload were significant decreases in relaxation times observed. The T2 relaxation time was the more reliable indicator of excessive levels of iron in the liver. The large range of T1 and T2 values encountered in normal volunteers precludes the use of MR to quantitatively measure iron levels in the liver. The T1 and T2 relaxation times measured at intervals for one individual tend to fluctuate as well, making the use of MR to follow the course of treatment of iron overload disorders unreliable.     

Nuclear magnetic resonance assessment of controlled hydrolysis of the capsular polysaccharides of Streptococcus pneumoniae serotypes 19A and 19F

Several glycoconjugate-based vaccines are inserted nowadays in infant vaccination schedules of most countries. In an initial stage, polysaccharides are modified under controlled conditions. The assessment of polysaccharide regions available for conjugation process after the hydrolysis is crucial to predict the conjugation results for achieving the final active pharmaceutical ingredient. Two hydrolyzed capsular polysaccharides were analyzed by a heteronuclear single-quantum correlation experiment. It was adjusted for assessing ³J_P-H to check the position of phosphate mono-ester residue after the hydrolysis process. All evaluated polysaccharides have been shown to remain with the anomeric position available for subsequent conjugation. The adjusted spectroscopic experiment was shown to be effective to study the hydrolysis of phosphate di-ester linked to capsular polysaccharides.     

Nuclear magnetic resonance study of ultrananocrystalline diamonds

We report on a nuclear magnetic resonance (NMR) study of ultrananocrystalline diamond (UNCD) materials produced by detonation technique. Analysis of the ¹³C and ¹H NMR spectra, spin-spin and spin-lattice relaxation times in purified UNCD samples is presented. Our measurements show that UNCD particles consist of a diamond core that is partially covered by a sp ²-carbon fullerene-like shell. The uncovered part of outer diamond surface comprises a number of hydrocarbon groups that saturate the dangling bonds. Our findings are discussed along with recent calculations of the UNCD structure. Significant increase in the spin-lattice relaxation rate (in comparison with that of natural diamond), as well as stretched exponential character of the magnetization recovery, are attributed to the interaction of nuclear spins with paramagnetic centers which are likely fabrication-driven dangling bonds with unpaired electrons. We show that these centers are located mainly at the interface between the diamond core and shell.     

Nuclear magnetic resonance of Nb in LiNbO3: effect of structural distortions on lineshapes

The expression for the angular dependence of the first moment of the nuclear magnetic resonance central transition (± 1/2 ↔ 1/2) lineshapes of a quadrupolar nuclei with half integer spins in a disordered solid is derived and used for investigation of the structural distortions in LiNbO₃.     

磁共振波谱及成像技术在纳米尺度物质生物效应研究中的应用

纳米尺度物质的生物效应研究是近年来在纳米科技发展过程中派生出来的一个崭新的、发展很快的且多学科高度交叉的领域，需要把纳米科学、物理学、化学以及生物医学等多学科的研究手段结合起来，进行综合研究．核磁共振波谱与成像，作为一种原位、无损、动态、实时、多信息的检测手段，在此领域的研究中将发挥不可或缺的重要作用．文章分3个方面简要介绍核磁共振波谱与成像技术在纳米尺度物质生物效应研究中的应用：（1）纳米尺度物质在生物组织及个体内的检测与分析；（2）纳米尺度物质与生物大分子相互作用的核磁共振波谱研究；（3）纳米尺度物质生物效应的核磁共振代谢组学研究．