The effect of instrument resolution on diffusion coefficients measured using NMR spectroscopy

This study presents a numerical simulation of the performance of an NMR spectrometer in which the influence of equipment with both low and high spatial resolutions is investigated. The results indicate that a low resolution NMR with a wide sensitivity curve may be unable to provide an accurate estimation of the moisture profile along the whole length of a test sample where the moisture gradient changes abruptly. It cannot provide accurate moisture information over a distance measured from each end of the test sample equivalent to the effective width of the sensitivity curve. However, a low-resolution spectrometer does not show any significant errors when calculating liquid diffusion coefficients, although the range of moisture contents over which they can be measured is limited. This study suggests that to avoid errors and practical difficulties, NMR spectrometers for moisture measurement should be selected carefully by matching the effective width of the sensitivity curve to the moisture properties of the material to be measured.

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Résumé Cette étude présente une simulation numérique de l'exécution d'un spectromètre RMN étudiant l'influence d'un matériel à basses et hautes résolutions spatiales. Les résultats indiquent qu'il se peut qu'une basse résolution du RMN avec une courbe large de sensibilité ne soit pas en mesure de fjurnir une évaluation précise du profil d'humidité sur la longueur entière d'un échantillon d'essai où le gradient d'humidité change soudainement. Il ne peut pas fournir d'informations précises sur l'humidité au-dessus d'une distance mesurée à partir de chaque extrémité de l'échantillon d'essai équivalant à la largeur effective de la courbe de sensibilité. Cependant, un spectromètre à basse résolution ne montre aucune erreur significative lors du calcul des coefficients de diffusion liquide, bien que l'intervalle du contenu d'humidité au-dessus duquel elles peuvent être mesurées soit limité. Cette étude suggère que pour éviter des erreurs et des difficulté pratiques, les spectromètres RMN mesurant l'humidité soient choisis soigneusement en associat la largeur effective de la courbe de sensibilité aux propriétés d'humidité du matériel à mesurer.

     

Characterization of aluminosilicate on rutile surface by high resolution solid state NMR

Pigments of titanium dioxide rutile, coated with SiO₂>-Al2O₃, have been characterized by high-resolution solid state NMR. The model samples were prepared following four synthesis routes differing by the aluminate and silicate salts addition sequence. From ²⁷Al single pulse MAS and 3Q-MAS NMR experiments, we characterize short range order around Al and distinguish several types of environment: Al_IV, Al_V, Al_VI and Al_VI linked to Ti, depending upon synthesis route and thermal treatment. The major difference between the different samples is observed after heat treatment at 750 °C. Rotational echo double resonance ²⁷Al-¹H and cross-polarization H-Si experiments provide longer range distance information through dipolar coupling to proton. Two types of surface treatment can be distinguished from ²⁷Al-¹H Redor by the presence of proton free alumina domain in the surface treatment.     

Multivariate curve resolution applied to the analysis and resolution of two-dimensional [1H,15N] NMR reaction spectra

Multivariate curve resolution is proposed for the study of complex chemical reactions monitored by two-dimensional (2D) NMR spectroscopy. In particular, in this work, multivariate curve resolution is applied to the study of the reaction between (15)N-labeled cisplatin and the amino acid-nucleotide hybrid (Phac-Met-linker-p(5')dG). At several stages of the reaction, 2D [(1)H,(15)N] HSQC NMR spectra were acquired and stored in data matrices. In a first step, multivariate curve resolution was applied to analyze individually each one of these 2D spectra, allowing the resolution of the corresponding (1)H and (15)N one-dimensional correlation spectra. In a second step, the whole set of 2D spectra recorded along the reaction were simultaneously analyzed by multivariate curve resolution, allowing the resolution of the kinetic concentration profiles and of the pure 2D NMR spectra of each of the species detected along the reaction. Results finally obtained confirmed previously postulated reaction mechanisms involving the existence of two monofunctional adducts and of two bifunctional adducts, with the structure of one of them not completely resolved.     

Ultra-high vacuum line components

Vacuum line components such as demountable seals, mechanical feed-throughs and valves suitable for ultra-high vacuum application are reviewed, with emphasis on the most recent developments.     

Structural studies of ideal organic-inorganic nanocomposites by high resolution diffractometry and NMR spectroscopy techniques

Hybrid organic-inorganic materials, silica-poly(ethylene glycol) (PEG) blends, were prepared by the sol-gel process from mixtures of tetraethoxysilane and PEG of low molecular mass. The synthesis scheme (acidic [HCl] or nucleophilic [NH₄F] catalysis) influences the structure of these materials and consequently their properties. Two different methods were used to investigate the structure of these blends: a) X-ray diffraction techniques; b) ²⁹Si NMR spectroscopy. A new x-ray diffractometry technique identifies precise interference functions and radial distribution functions of these blends. The comparison of predicted radial distribution functions of the Bell and Dean's physical model refined by Gaskell with the radial distribution function obtained from this technique is implemented to identify the structure of these blends. Analysis by amorphography has identified the existence of SiO₂ silica grains and provides only about the positional disorder of these grains in continuum random network. The NMR spectroscopy discriminates the different silicon sites and demonstrates the changes of the morphology and structure when the nature of the catalyst is modified. These results indicate that the structure of non-crystalline SiO₂ aggregates inside nanocomposites differs from fused glass by their compositional disorders. These nanocomposites could be described as an agglomerate of SiO₂ objects with the pores filled by disordered polymer chains. When these materials are obtained under acidic conditions, the polymer chains are linked to the SiO₂ grains forming an ideal composite.     

A cluster expansion method for the complete resolution of microscopic ionization equilibria from NMR titrations

The NMR chemical shift of spin 1/2 nuclei in a polyprotic molecule represents a sensitive probe of microscopic protonation equilibria. However, these equilibria are commonly parametrized in terms of microscopic equilibrium constants, whose number increases very rapidly with the number of ionizable groups. For that reason their determination was considered to be basically impossible except for the cases of the simplest molecules. On the basis of a cluster expansion of the free energy of a microstate, we propose a novel parametrization of this problem that drastically reduces the number of necessary parameters needed to specify the microscopic equilibria. Such cluster parameters can be extracted from NMR titration data in a straightforward way. Once these parameters are known, all microscopic equilibrium constants can be obtained.     

超高纯乙烯的制备

综述了超高纯乙烯(C2H4)的制备工艺,提出了通过精馏加吸附的纯化方法,将含有氧(O2)、二氧化碳(CO2)、一氧化碳(CO)、乙烷(C2 H6)、乙炔(C2 H2)、氢气(H2)、甲烷(CH4)、碳三及以上等杂质的粗C2 H4提纯到99.9995％以上.利用Aspen Plus模拟软件分析,确定超高纯C2 H4制备的...     

Evaluation of high resolution magic-angle coil spinning NMR spectroscopy for metabolic profiling of nanoliter tissue biopsies

High-resolution magic-angle sample spinning (HR-MAS) (1)H NMR spectroscopy of tissue biopsies combined with chemometric techniques has emerged as a valuable methodology for disease diagnosis and environmental assessments. However, the tissue mass required for such experiments is of the order of 10 mg, and this can compromise the metabolic evaluation because of tissue heterogeneity. Tissue availability is often a limitation for clinical studies due to histopathological requirements, which are currently the gold standard for diagnosis, for example, in the case of tumors. Here, we introduce the use of a rotating micro-NMR detector that optimizes the coil filling factor such that mass-limited samples can be measured. We show the results for measuring nanoliter volume tissue biopsies using a commercial HR-MAS probe for the first time. The method has been tested with bovine muscle and human gastric mucosal tumor tissue samples. The gain in mass sensitivity is approximate up to 17-fold, and the adequate spectral resolution (3 Hz) allows the measurement of the metabolite profiles in nanoliter volume samples, thereby limiting the ambiguity resulting from heterogeneous tissues; thus, the approach presents diagnostic potential for studies by metabonomics of mass-limited biopsies.     

高合金超高强度钢的发展

超高强度钢是在普通合金结构钢的基础上发展起来的一种超高强度、高韧性合金钢,在现代工业中占有重要地位,在航空、航天部门也被广泛使用.本文介绍了超高强度钢,特别是高合金超高强度钢的发展和应用情况,指出了现今在这一领域的研究热点.     

HIRFL-CSR超高真空烘烤系统

为了满足兰州重离子加速器冷却储存环 6× 10 - 9Pa的真空度要求 ,必须建立温度在 2 0 0～ 30 0℃、控制良好的在线烘烤系统。主要从热电偶、加热器及绝热套 ;功率计算及分布 ;烘烤控制 ;样机测试结果等几个方面介绍兰州重离子加速器冷却储存环 (HIRFL- CSR)超高真空烘烤系统。     

The International Symposium on Ultra-high Temperature Materials

An encapsulation technique for high-temperature controlled-environment testing is introduced. This encapsulation technique is combined with the DC potential drop technique to monitor the crack growth during the experiment. This technique eliminates the complicated retort systems of conventional mechanical testing and possesses the advantages of compactness, transportability, ease of manufacture and low cost. Test results in vacuum using this technique are compared with results of similar experiments in air and in a retort system.     

陀螺输出信号的超高速处理

采用硬件描述语言VHDL设计了专用于方向余弦阵计算的集成电路,可用于对激光陀螺或挠性陀螺输出的脉冲信号或脉宽调制信号进行方向余弦阵计算。输入脉冲频率最高可达1 MHz;分辨力为1.57＂时,最大角速率可达400(°)/s。方向余弦阵的元素采用64位有符号定点数表示,计算精度达1.08×10-19。硬件结构采用64位宽度的循环移位链,核心计算单元由46个8位加法器构成3级流水线并行处理。     

超高密度磁记录介质的研究进展

总结了近年来超高密度磁记录介质的研究概况,着重介绍了垂直磁记录介质中L10相FePt薄膜的研究方法,并认为L10相FePt薄膜将会成为高密度磁盘记录介质的主流.倾斜磁记录、热辅助磁记录、图案记录等存储技术,目前处于实验室研究阶段,但是有望突破垂直磁记录的超顺磁极限,实现超高密度磁记录.