共查询到19条相似文献，搜索用时 140 毫秒
1.
高分辨核磁共振（Nuclear Magnetic Resonance,NMR）波谱是一种能够在非侵入性状态下获得生物组织分子信息的有效手段.分子间多量子相干（intermolecular Multiple-Quantum Coherence,iMQC）信号源于分子间的远程偶极相互作用,仅依赖于偶极相关距离内的磁场相对均匀性,因此可用于在不均匀磁场下获得高分辨的NMR谱.文中简要介绍了iMQC的发展历程及现状,并主要讨论了iMQC方法及其在活体及生物组织中的应用.虽然iMQC目前应用在老鼠身上比较常见,但最近的研究表明iMQC方法已被用于人体小脑的研究,将来iMQC方法将有可能应用于人体的其他器官以及其他的动物研究,具有广阔的发展前景. 相似文献
2.
本文研究单模场中两个原子之间的偶极相互作用对系统本征能量的影响，并比较了计及原子间偶极作用与忽略原子间仍极作用时光子数的期望值． 相似文献
3.
两等同双能级原子与三模腔场任意多光子共振相互作用辐射谱的一般特征 总被引：3，自引：0，他引：3
本文研究了两个偶极——偶极力关联的等同双能级原子与三模腔场间任意多光于共振相互作用的辐射谱。对三模腔场分别处于不同数态:即三模均为真空场、三模均为强场、一模为真空场两模为强场以及两模为真空场一模为强场时辐射谱的结构特征及物理特性进行了详细分析,从而揭示出“三模腔场——两原子系统”的多光子辐射谱的一般特征。 相似文献
5.
用两格点分子场理论对Ce_2Fe_（17）X(X=0,D_(4.8),N_3)合金(或金属间化合物)的饱和磁化与温度的关系进行了分析,通过对实验数据的拟合计算得到了分子场系数n_(cc)、n_(CF)、n_(FF),计算出了居里温度,给出了各个磁化强度以及分子场强度随温度变化的曲线. 相似文献
6.
本文利用手性合成子4-(L)-孟氧基丁烯内酯作为亲偶极体,与芳环类的腈氧化物偶极体系通过1,3偶极环加成反应合成了手性异噁唑啉-2-羟基苯基衍生物。化合物结构经元素及波谱分析、IR、1H NMR、13C NMR及MS得到确证。 相似文献
7.
一、离子的极化 对一个单独的离子来说,它所带的电荷数等于其正负电荷数<核电荷和电子数>的代数和。然而它的正负电荷中心却是重叠的,因此离子就不存在有偶极<瞬时偶极除外>(图1)。离子的核外电子是有各种的运动状态<俗称电子云>,这使它象一个柔性球一样具有变形性。若把它置于一个正电场<或负电场>之中,在电场力诱导 相似文献
8.
介绍了中心势场中的束缚态Schr(o)dinger方程的数值求解方法,并以重夸克偶素cc-为例进行了数值计算,得到的结果能与实验值较好的吻合. 相似文献
9.
本文利用晶场理论中的点电荷-电偶极模型,从“孤立络离子”近似下Cu~(2+)的光学性质和磁学性质的研究出发,探讨了晶体中Cu~(2+)-Cu~(2+)离子间相互作用对电子顺磁共振谱(EPR)的影响。以Cu(detc)_2晶体为例,首次用SCF-d轨道理论,解释了前人没法定量解释的零场分裂现象,建立了考虑Cu~(2+)-Cu~(2+)间相互作用后自旋哈密顿参量和晶格参数间的关系,从而首次从理论上给出了从孤立络离子近似到存在离子间相互作用时晶体的EPR谱的统一解释。计算结果表明:对于Cu(detc)_2,考虑Cu~(2+)-Cu~(2+)对的影响后,g-因子不变(这与实验结果符合),而零场分裂主要是旋轨耦合、晶场对称性以及Cu~(2+)-Cu~(2+)对间交换作用联合作用的结果。并对所得结果进行了讨论。 相似文献
10.
一、原理: 极性分子电子云分布不均匀,分子内部正负电荷中心不重合,即出现偶极;非极性分子则相反。因此利用静电诱导作用,由箔验电器箔片是否闭合,能够推测该物质的分子是否具有极性。 相似文献
11.
李传生曾寿金许明三刘广何伟辉 《福建工程学院学报》2021,(4):349-355
基于三周期极小曲面(TPMS)设计5种不同孔隙率梯度分布的梯度多孔支架,利用选区激光熔化(SLM)技术制造Ti6Al4V梯度多孔支架。该支架具有类似于人骨梯度多孔结构的梯度孔隙率。压缩测试结果表明,5种梯度多孔支架的弹性模量为8.75~13.88 GPa,抗压强度为219.48~ 528.21 MPa,符合承载骨的弹性模量和抗压强度要求。弹性模量和抗压强度都随着平均孔隙率P- (或边缘孔隙率PB )的增大而减小,P-对弹性模量和抗压强度的影响大于PB。采用Gibson-Ashby的拟合结果可以为承载骨的设计提供参考。 相似文献
12.
磁共振成像技术依据原子核能级跃迁释放能量在物质不同结构环境中不同的衰减,通过外加梯度磁场检测所发射的电磁波,获得构成物体的原子核种类和位置,从而绘制出物体内部的结构图像．近年来,随着快速变化的梯度磁场的应用,核磁共振成像技术不仅在医学,而且在其他科研领域都得到了广泛的应用． 相似文献
13.
Rabbits were trained in either positive patterning (AX+, A−, X−) or negative patterning (A+, X+, AX−) using one of four intervals between the onset of A and the onset of X on AX trials. These intervals were 0, 800, 2,400, and 5,600 msec. In each task, all groups acquired an appropriate pattern of discriminative responding. Following acquisition, all rabbits were tested with the four different A-X intervals. All positive patterning groups showed an excitatory gradient, in which the highest level of responding occurred at the interval used in training. Conversely, all but one of the negative patterning groups showed an inhibitory gradient, in which the lowest level of responding occurred at the interval used in training. The one exception was the negative patterning group trained with simultaneous AX stimuli (0 msec), which showed a low, broad gradient, indicating transfer of inhibition across all the intervals. The results are discussed with respect to temporal encoding mechanisms and accounts of conditional discriminations. 相似文献
14.
Two experiments were performed to investigate the relationship between excitatory stimulus control (number of responses to a training stimulus) and dimensional stimulus control (generalization gradient slope). In experiment 1, after being trained to peck a green key, pigeons received either 20, 40, or 80 brief (.5, 2, 4, or 8 sec) presentations of a 45-deg line followed by reinforcement (12 groups) or 20, 40, or 80 reinforcements for pecking a continuously presented 45-deg line (3 groups). Number of reinforcements determined the slope (percent of total responses to 45 deg) of a subsequent line-angle generalization gradient, but number of responses to the 45-deg line in the test was controlled by total experience with 45 deg as measured by either total exposure time or total responses to 45 deg in training. In a second experiment, it was shown that increasing the number of days of pretraining to green decreased the slope of the gradient (in subjects given 2-sec presentations), but had no effect on number of responses to 45 deg in the test. Furthermore, continuous presentation yielded flatter gradients but more responding to the 45-deg line in the test than did 2-sec presentations. It was concluded that the measures of dimensional stimulus control and excitatory stimulus control reflect different processes because they vary differentially (sometimes in different directions) in response to the same independent variable manipulations. 相似文献
15.
对戴云山600 m常绿阔叶林（EBF）、1000 m针叶林（CF）、1400 m亚高山矮林（SDF）、1800 m高山草甸（AM）4种不同海拔森林类型土壤理化性质与酶活性进行研究。结果表明：4个不同海拔森林类型土壤理化性质和酶活性存在明显差异,5种土壤酶活性在不同海拔森林类型土壤剖面中均呈现自上而下递减的规律,磷酸单酯酶活性在4个不同森林类型间均呈显著差异;蔗糖酶、脲酶、过氧化酶活性在EBF、CF间呈显著差异,相关性分析可知,5种土壤酶与TN、HN、TP、AK、OM呈极显著或显著正相关,与土壤pH值呈极显著负相关,表明土壤酶活性在不同海拔森林类型土壤养分变化中发挥着重要作用。研究揭示了土壤酶活性与土壤理化性质在不同海拔森林类型之间的差异及其空间分布特点,分析了土壤酶与土壤理化性质的关系,为了解森林土壤肥力总体状况提供理论依据。 相似文献
16.
结构层淀积是MEMS加工过程中的重要工艺步骤,淀积薄膜的应力梯度是影响MEMS器件性能的一个重要的力学参数．文中介绍了几种常见的平均应力梯度在线测量方法,阐明了其测试结构及测量原理,并对这些测量方法进行了比较． 相似文献
17.
A kind of image distortion in Optical Coherence Tomography (OCT) resulted from average refractive index changes between structures of bio-tissue is discussed for the first time. Analysis is given on following situations:1) Exact refraction index changes between mierostruetures;2)The gradient of average refractive index change between different tissue layers is parallel to the probe beam;3) The gradient of average refractive index change is vertical to the probe beam. The results show that the image distortion of situation 1) is usually negligible ;in situation 2) there is a spread or shrink effect without relative location error; however, in situation 3)there is a significant image error inducing relative location displacement between different structures. Preliminary design to eliminate the distortion is presented, the method of which mainly based on the image classification and pixel array re-arrangement. 相似文献
18.
In this study, an artificial neural network （ANN） model for studying the strength properties of steel fiber reinforced concrete （SFRC） containing fly ash was devised. The mixtures were prepared with 0 wt%, 15 wt%, and 30 wt% of fly ash, at 0 vol.%, 0.5 vol.%, 1.0 vol.% and 1.5 vol.% of fiber, respectively. After being cured under the standard conditions for 7, 28, 90 and 365 d, the specimens of each mixture were tested to determine the corresponding compressive and flexural strengths. The pa- rameters such as the amounts of cement, fly ash replacement, sand, gravel, steel fiber, and the age of samples were selected as input variables, while the compressive and flexural strengths of the concrete were chosen as the output variables. The back propagation learning algorithm with three different variants, namely the Levenberg-Marquardt （LM）, scaled conjugate gradient （SCG） and Fletcher-Powell conjugate gradient （CGF） algorithms were used in the network so that the best approach can be found. The results obtained from the model and the experiments were compared, and it was found that the suitable algorithm is the LM algorithm. Furthermore, the analysis of variance （ANOVA） method was used to determine how importantly the experimental parameters affect the strength of these mixtures. 相似文献
19.
Distribution of Bacterial Communities in Petroleum-Contaminated Soils from the Dagang Oilfield,China
Diversity in bacterial communities was investigated along a petroleum hydrocarbon content gradient (0–0.4043 g/g) in surface (5–10 cm) and subsurface (35–40 cm) petroleum-contaminated soil samples from the Dagang Oilfield, China. Using 16S rRNA Illumina high-throughput sequencing technology and several statistical methods, the bacterial diversity of the soil was studied. Subsequently, the environmental parameters were measured to analyze its relationship with the community variation. Nonmetric multidimensional scaling and analysis of similarities indicated a significant difference in the structure of the bacterial community between the nonpetroleum-contaminated surface and subsurface soils, but no differences were observed in different depths of petroleum-contaminated soil. Meanwhile, many significant correlations were obtained between diversity in soil bacterial community and physicochemical properties. Total petroleum hydrocarbon, total organic carbon, and total nitrogen were the three important factors that had the greatest impacts on the bacterial community distribution in the long-term petroleum-contaminated soils. Our research has provided references for the bacterial community distribution along a petroleum gradient in both surface and subsurface petroleum-contaminated soils of oilfield areas. 相似文献