Time-Domain Quantification of Multiple-Quantum-Filtered Na Signal Using Continuous Wavelet Transform Analysis

The application of continuous wavelet transform (CWT) analysis technique is presented to analyze multiple-quantum-filtered (MQF) ²³Na magnetic resonance spectroscopy (MRS) data. CWT acts on the free-induction-decay (FID) signal as a time-frequency variable filter. The signal-to-noise ratio (SNR) and frequency resolution of the output filter are locally increased. As a result, MQF equilibrium longitudinal magnetization and the apparent fast and slow transverse relaxation times are accurately estimated. A developed iterative algorithm based on frequency signal detection and components extraction, already proposed, was used to estimate the values of the signal parameters by analyzing simulated time-domain MQF signals and data from an agarose gel. The results obtained were compared to those obtained by measurement of signal height in frequency domain as a function of MQF preparation time and those obtained by a simple time-domain curve fitting. The comparison indicates that the CWT approach provides better results than the other tested methods that are generally used for MQF ²³Na MRS data analysis, especially when the SNR is low. The mean error on the estimated values of the amplitude signal and the apparent fast and slow transverse relaxation times for the simulated data were 2.19, 6.63, and 16.17% for CWT, signal height in frequency domain, and time-domain curve fitting methods, respectively. Another major advantage of the proposed technique is that it allows quantification of MQF ²³Na signal from a single FID and, thus, reduces the experiment time dramatically.     

Fluid and plastic flow dynamics of the critical state for a strongly pinned 2D superconductor

The frequency of the Raman active A_1g radial breathing mode has been widely used as a tool to estimate the distribution of diameters of single wall carbon nanotubes (SWNT). However, the relation between frequency and diameter is not straightforward and results are model-dependent. Because most of the experiments are performed on bundles and not on isolated tubes, the model should especially take into account the van der Waals intertube interactions. Here, we use a pair-potential approach to account for such interactions and we derive a nonlinear relation between the SWNT diameter and the frequency of the A_1g radial breathing modes. We demonstrate a good agreement between calculations and the diameters derived from diffraction experiments on the same samples. Received 22 December 1999 and Received in final form 17 July 2000     

Na1.0Zn1.62Si1.38O4.84·0.6H2O的水热合成及离子导电性质

Anew sodium zincosilicate single crystal Na_1.0Zn_1.62Si_1.38O_4.84·0.6H₂O with size of 0.3mm×0.3mm×0.3 mm was prepared by hydrothermal synthesis method. Powder X-ray diffraction analysis result shows that this compound is a new phase.The compound is stable up to 500℃. The results of ACimpedance measurement shows that its ionic conductivity at 450℃ is 2×10^-4S·cm^-1 and the activation energy for ionic conduction is 79.64 KJ/mol.     

钠硫电池电极结构改进与电池性能研究

研究了新型的钠硫电池钠极钠芯结构和硫极预制结构对电池性能影响．实验表明,钠极的钠芯结构不仅能改善电池放电性能,而且有利提高电池的比能量和安全性;内衬氧化铝纤维的硫极预制结构能缓和界面极化,改善电池充电性能．改进电极结构后的钠硫电池也有利于电池向商品化,实用性发展     

Raman spectroscopy on single- and multi-walled nanotubes under high pressure

The pressure dependence of the high-energy Raman modes in single- and multi-walled carbon nanotubes was measured in the range 0–10 GPa. We found the pressure coefficient to be linear in both materials but 25% smaller in MWNT. Given that the curvature effects on vibrational properties of the rolled-up graphene sheets are small, we can explain this difference simply with elasticity theory. Received: 17 May 1999 / Accepted 18 May 1999 / Published online: 4 August 1999     

分光光度法测定土壤中碘的方法改进

对碳酸钠-氧化锌熔矿,分光光度法测定土壤样品中碘含量的方法进行改进,在不经过超级恒温水浴的情况下,对熔样温度、试剂用量的选择、比色温度等实验条件进行优化。改进后的方法经过国家一级标准物质分析验证,准确度ΔlgC0.05,相对标准偏差(RSD)10%,结果准确可靠,完全满足地球化学调查样品中对碘的质量要求,更加适合批量生产。     

M2Ga6Te10 (M: Li,Na): Two New Non‐metallic Filled β‐Manganese Phases – X‐ray and NMR Studies

Two new non‐metallic filled β‐manganese phases M₂Ga₆Te₁₀ (M: Li, Na) are obtained as black, homogeneous, microcristalline samples as well as single crystals by direct reaction of the elements. According to the single crystal structure determinations both compounds crystallize in space group R32 (No. 155, Z = 2) with the lattice constants: a = 1436.9(2), c = 1759.0(4) pm (T = 180 K, Li₂Ga₆Te₁₀) and a = 1458(1) pm, c = 1776.1(4) pm (T = 290 K, Na₂Ga₆Te₁₀). Their structures are characterized by tetrahedral close packings of Te^2–, corresponding to the arrangement of Mn atoms in β‐Mn. While Ga³⁺ ions are distributed in an ordered way over 12% of the tetrahedral holes, the M⁺ ions occupy all distorted octahedral (“metaprismatic”) holes. As the Li⁺ ions are too small they occupy off‐center positions inside the metaprisms. Positions with the strongest off‐centering can only be refined on the basis of a split model. MAS‐NMR measurements, including multiple quantum NMR, allowed the two different crystallographic M⁺ sites to be distinguished unambigously by separate ⁷Li and ²³Na signals, respectively. The assignment of the NMR signals was supported by measurements of samples in which Li⁺ was partly substituted by larger cations (Sn²⁺, Pb²⁺).     

The Mixed Valence Tungsten(IV,V) Compound Na[W2O2Br6]

The reaction of W₆Br₁₂, NaBr, and WO₂Br₂ in the presence of Br₂ in a sealed silica tube yields Na[W₂O₂Br₆] together with WOBr₄ and WO₂Br₂ in the low temperature zone (temperature gradient 1030/870 K). Na[W₂O₂Br₆] crystallizes orthorhombically in the space group Immm (no. 71) with a = 3.775 Å, b = 10.400 Å, c = 13.005 Å and Z = 2. Pairs of condensed trans-[WO₂Br₄] octahedra with a common Br₂ edge form along [100] double chains [W₂O_4/2Br₆]^1– via the oxygen atoms. The mixed valent tungsten atoms are bonded to W₂ pairs with a 2 c–3 e bond (d(W–W) = 2.946 Å, d(W–O) = 1.888 Å, d(W–Br^b) = 2.537 Å, d(W–Br^t) = 2.535 Å, ∢O–W–O = 177.4°, ∢Br^b–W–Br^b (endocyclic) = 109.0°). The Na⁺ cations connect the anionic double chains to form two-dimensional layers parallel (001), which interact by van der Waals forces. The cations are eightfold coordinated by a cube of the terminal Br^t ligands of the polymeric anions (d(Na–Br) = 3.138 Å). Na[W₂O₂Br₆] may be discussed as an intercalation compound of the oxide bromide WOBr₃.     

ChemInform Abstract: Ab initio Study of the Molecular Structure of Oxo and Thio Salts LAB3 (L: Li and Na; A: N,P, and S+; and B: O and S).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Potassium‐Sodium‐Niobate‐Based Thin Films: Lead Free for Micro‐Piezoelectrics

Extensive research and great progress of (K,Na)NbO₃ (KNN)‐based lead‐free piezoelectric films have been driven by the current legislation and the requirement for sustainable development of society and environment in the applications of microelectromechanical systems. A comprehensive discussion of the recent achievement in KNN‐based films is presented herein. First, the available synthetic techniques, chemical modification, the ferroelectric and piezoelectric properties of KNN‐based films are reviewed, followed by an introduction of the crystal structures and electrical properties of KNN‐based epitaxial films in comparison with the bulk ceramics. Finally, the applications of KNN‐based films for the sensors, the energy harvesters, and energy storage devices are addressed, and current challenges and prospects for future work are discussed.